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Article Contents

Introduction, physiological effects of dehydration, hydration and chronic diseases, water consumption and requirements and relationships to total energy intake, water requirements: evaluation of the adequacy of water intake, acknowledgments, water, hydration, and health.

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Barry M Popkin, Kristen E D'Anci, Irwin H Rosenberg, Water, hydration, and health, Nutrition Reviews , Volume 68, Issue 8, 1 August 2010, Pages 439–458, https://doi.org/10.1111/j.1753-4887.2010.00304.x

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This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Water is essential for life. From the time that primeval species ventured from the oceans to live on land, a major key to survival has been the prevention of dehydration. The critical adaptations cross an array of species, including man. Without water, humans can survive only for days. Water comprises from 75% body weight in infants to 55% in the elderly and is essential for cellular homeostasis and life. 1 Nevertheless, there are many unanswered questions about this most essential component of our body and our diet. This review attempts to provide some sense of our current knowledge of water, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, the effects of variation in water intake on health and energy intake, weight, and human performance and functioning.

Recent statements on water requirements have been based on retrospective recall of water intake from food and beverages among healthy, noninstitutionalized individuals. Provided here are examples of water intake assessment in populations to clarify the need for experimental studies. Beyond these circumstances of dehydration, it is not fully understood how hydration affects health and well-being, even the impact of water intakes on chronic diseases. Recently, Jéquier and Constant 2 addressed this question based on human physiology, but more knowledge is required about the extent to which water intake might be important for disease prevention and health promotion.

As noted later in the text, few countries have developed water requirements and those that exist are based on weak population-level measures of water intake and urine osmolality. 3 , 4 The European Food Safety Authority (EFSA) was recently asked to revise existing recommended intakes of essential substances with a physiological effect, including water since this nutrient is essential for life and health. 5

The US Dietary Recommendations for water are based on median water intakes with no use of measurements of the dehydration status of the population to assist. One-time collection of blood samples for the analysis of serum osmolality has been used by the National Health and Nutrition Examination Survey program. At the population level, there is no accepted method of assessing hydration status, and one measure some scholars use, hypertonicity, is not even linked with hydration in the same direction for all age groups. 6 Urine indices are used often but these reflect the recent volume of fluid consumed rather than a state of hydration. 7 Many scholars use urine osmolality to measure recent hydration status. 8 , – 12 Deuterium dilution techniques (isotopic dilution with D 2 O, or deuterium oxide) allow measurement of total body water but not water balance status. 13 Currently, there are no completely adequate biomarkers to measure hydration status at the population level.

In discussing water, the focus is first and foremost on all types of water, whether it be soft or hard, spring or well, carbonated or distilled. Furthermore, water is not only consumed directly as a beverage; it is also obtained from food and to a very small extent from oxidation of macronutrients (metabolic water). The proportion of water that comes from beverages and food varies according to the proportion of fruits and vegetables in the diet. The ranges of water content in various foods are presented in Table 1 . In the United States it is estimated that about 22% of water intake comes from food while the percentages are much higher in European countries, particularly a country like Greece with its higher intake of fruits and vegetables, or in South Korea. 3 , – 15 The only in-depth study performed in the United States of water use and water intrinsic to food found a 20.7% contribution from food water; 16 , 17 however, as shown below, this research was dependent on poor overall assessment of water intake.

Ranges of water content for selected foods.

Data from the USDA national nutrient database for standard reference, release 21, as provided in Altman. 126

This review considers water requirements in the context of recent efforts to assess water intake in US populations. The relationship between water and calorie intake is explored both for insights into the possible displacement of calories from sweetened beverages by water and to examine the possibility that water requirements would be better expressed in relation to calorie/energy requirements with the dependence of the latter on age, size, gender, and physical activity level. Current understanding of the exquisitely complex and sensitive system that protects land animals against dehydration is covered and commentary is provided on the complications of acute and chronic dehydration in man, against which a better expression of water requirements might complement the physiological control of thirst. Indeed, the fine intrinsic regulation of hydration and water intake in individuals mitigates prevalent underhydration in populations and its effects on function and disease.

Regulation of fluid intake

To prevent dehydration, reptiles, birds, vertebrates, and all land animals have evolved an exquisitely sensitive network of physiological controls to maintain body water and fluid intake by thirst. Humans may drink for various reasons, particularly for hedonic ones, but drinking is most often due to water deficiency that triggers the so-called regulatory or physiological thirst. The mechanism of thirst is quite well understood today and the reason nonregulatory drinking is often encountered is related to the large capacity of the kidneys to rapidly eliminate excesses of water or to reduce urine secretion to temporarily economize on water. 1 But this excretory process can only postpone the necessity of drinking or of ceasing to drink an excess of water. Nonregulatory drinking is often confusing, particularly in wealthy societies that have highly palatable drinks or fluids that contain other substances the drinker seeks. The most common of these are sweeteners or alcohol for which water is used as a vehicle. Drinking these beverages is not due to excessive thirst or hyperdipsia, as can be shown by offering pure water to individuals instead and finding out that the same drinker is in fact hypodipsic (characterized by abnormally diminished thirst). 1

Fluid balance of the two compartments

Maintaining a constant water and mineral balance requires the coordination of sensitive detectors at different sites in the body linked by neural pathways with integrative centers in the brain that process this information. These centers are also sensitive to humoral factors (neurohormones) produced for the adjustment of diuresis, natriuresis, and blood pressure (angiotensin mineralocorticoids, vasopressin, atrial natriuretic factor). Instructions from the integrative centers to the “executive organs” (kidney, sweat glands, and salivary glands) and to the part of the brain responsible for corrective actions such as drinking are conveyed by certain nerves in addition to the above-mentioned substances. 1

Most of the components of fluid balance are controlled by homeostatic mechanisms responding to the state of body water. These mechanisms are sensitive and precise, and are activated with deficits or excesses of water amounting to only a few hundred milliliters. A water deficit produces an increase in the ionic concentration of the extracellular compartment, which takes water from the intracellular compartment causing cells to shrink. This shrinkage is detected by two types of brain sensors, one controlling drinking and the other controlling the excretion of urine by sending a message to the kidneys, mainly via the antidiuretic hormone vasopressin to produce a smaller volume of more concentrated urine. 18 When the body contains an excess of water, the reverse processes occur: the lower ionic concentration of body fluids allows more water to reach the intracellular compartment. The cells imbibe, drinking is inhibited, and the kidneys excrete more water.

The kidneys thus play a key role in regulating fluid balance. As discussed later, the kidneys function more efficiently in the presence of an abundant water supply. If the kidneys economize on water and produce more concentrated urine, they expend a greater amount of energy and incur more wear on their tissues. This is especially likely to occur when the kidneys are under stress, e.g., when the diet contains excessive amounts of salt or toxic substances that need to be eliminated. Consequently, drinking a sufficient amount of water helps protect this vital organ.

Regulatory drinking

Most drinking occurs in response to signals of water deficit. Apart from urinary excretion, the other main fluid regulatory process is drinking, which is mediated through the sensation of thirst. There are two distinct mechanisms of physiological thirst: the intracellular and the extracellular mechanisms. When water alone is lost, ionic concentration increases. As a result, the intracellular space yields some of its water to the extracellular compartment. Once again, the resulting shrinkage of cells is detected by brain receptors that send hormonal messages to induce drinking. This association with receptors that govern extracellular volume is accompanied by an enhancement of appetite for salt. Thus, people who have been sweating copiously prefer drinks that are relatively rich in Na+ salts rather than pure water. When excessive sweating is experienced, it is also important to supplement drinks with additional salt.

The brain's decision to start or stop drinking and to choose the appropriate drink is made before the ingested fluid can reach the intra- and extracellular compartments. The taste buds in the mouth send messages to the brain about the nature, and especially the salt content, of the ingested fluid, and neuronal responses are triggered as if the incoming water had already reached the bloodstream. These are the so-called anticipatory reflexes: they cannot be entirely “cephalic reflexes” because they arise from the gut as well as the mouth. 1

The anterior hypothalamus and pre-optic area are equipped with osmoreceptors related to drinking. Neurons in these regions show enhanced firing when the inner milieu gets hyperosmotic. Their firing decreases when water is loaded in the carotid artery that irrigates the neurons. It is remarkable that the same decrease in firing in the same neurons takes place when the water load is applied on the tongue instead of being injected into the carotid artery. This anticipatory drop in firing is due to communication from neural pathways that depart from the mouth and converge onto neurons that simultaneously sense the blood's inner milieu.

Nonregulatory drinking

Although everyone experiences thirst from time to time, it plays little role in the day-to-day control of water intake in healthy people living in temperate climates. In these regions, people generally consume fluids not to quench thirst, but as components of everyday foods (e.g., soup, milk), as beverages used as mild stimulants (tea, coffee), and for pure pleasure. A common example is alcohol consumption, which can increase individual pleasure and stimulate social interaction. Drinks are also consumed for their energy content, as in soft drinks and milk, and are used in warm weather for cooling and in cold weather for warming. Such drinking seems to also be mediated through the taste buds, which communicate with the brain in a kind of “reward system”, the mechanisms of which are just beginning to be understood. This bias in the way human beings rehydrate themselves may be advantageous because it allows water losses to be replaced before thirst-producing dehydration takes place. Unfortunately, this bias also carries some disadvantages. Drinking fluids other than water can contribute to an intake of caloric nutrients in excess of requirements, or in alcohol consumption that, in some people, may insidiously bring about dependence. For example, total fluid intake increased from 79 fluid ounces in 1989 to 100 fluid ounces in 2002 among US adults, with the difference representing intake of caloric beverages. 19

Effects of aging on fluid intake regulation

The thirst and fluid ingestion responses of older persons to a number of stimuli have been compared to those of younger persons. 20 Following water deprivation, older individuals are less thirsty and drink less fluid compared to younger persons. 21 , 22 The decrease in fluid consumption is predominantly due to a decrease in thirst, as the relationship between thirst and fluid intake is the same in young and old persons. Older persons drink insufficient amounts of water following fluid deprivation to replenish their body water deficit. 23 When dehydrated older persons are offered a highly palatable selection of drinks, this also fails to result in increased fluid intake. 23 The effects of increased thirst in response to an osmotic load have yielded variable responses, with one group reporting reduced osmotic thirst in older individuals 24 and one failing to find a difference. In a third study, young individuals ingested almost twice as much fluid as old persons, even though the older subjects had a much higher serum osmolality. 25

Overall, these studies support small changes in the regulation of thirst and fluid intake with aging. Defects in both osmoreceptors and baroreceptors appear to exist as do changes in the central regulatory mechanisms mediated by opioid receptors. 26 Because the elderly have low water reserves, it may be prudent for them to learn to drink regularly when not thirsty and to moderately increase their salt intake when they sweat. Better education on these principles may help prevent sudden hypotension and stroke or abnormal fatigue, which can lead to a vicious circle and eventually hospitalization.

Thermoregulation

Hydration status is critical to the body's process of temperature control. Body water loss through sweat is an important cooling mechanism in hot climates and in periods of physical activity. Sweat production is dependent upon environmental temperature and humidity, activity levels, and type of clothing worn. Water losses via skin (both insensible perspiration and sweating) can range from 0.3 L/h in sedentary conditions to 2.0 L/h in high activity in the heat, and intake requirements range from 2.5 to just over 3 L/day in adults under normal conditions, and can reach 6 L/day with high extremes of heat and activity. 27 , 28 Evaporation of sweat from the body results in cooling of the skin. However, if sweat loss is not compensated for with fluid intake, especially during vigorous physical activity, a hypohydrated state can occur with concomitant increases in core body temperature. Hypohydration from sweating results in a loss of electrolytes, as well as a reduction in plasma volume, and this can lead to increased plasma osmolality. During this state of reduced plasma volume and increased plasma osmolality, sweat output becomes insufficient to offset increases in core temperature. When fluids are given to maintain euhydration, sweating remains an effective compensation for increased core temperatures. With repeated exposure to hot environments, the body adapts to heat stress and cardiac output and stroke volume return to normal, sodium loss is conserved, and the risk for heat-stress-related illness is reduced. 29 Increasing water intake during this process of heat acclimatization will not shorten the time needed to adapt to the heat, but mild dehydration during this time may be of concern and is associated with elevations in cortisol, increased sweating, and electrolyte imbalances. 29

Children and the elderly have differing responses to ambient temperature and different thermoregulatory concerns than healthy adults. Children in warm climates may be more susceptible to heat illness than adults due to their greater surface area to body mass ratio, lower rate of sweating, and slower rate of acclimatization to heat. 30 , 31 Children may respond to hypohydration during activity with a higher relative increase in core temperature than adults, 32 and with a lower propensity to sweat, thus losing some of the benefits of evaporative cooling. However, it has been argued that children can dissipate a greater proportion of body heat via dry heat loss, and the concomitant lack of sweating provides a beneficial means of conserving water under heat stress. 30 Elders, in response to cold stress, show impairments in thermoregulatory vasoconstriction, and body water is shunted from plasma into the interstitial and intracellular compartments. 33 , 34 With respect to heat stress, water lost through sweating decreases the water content of plasma, and the elderly are less able to compensate for increased blood viscosity. 33 Not only do they have a physiological hypodipsia, but this can be exaggerated by central nervous system disease 35 and by dementia. 36 In addition, illness and limitations in daily living activities can further limit fluid intake. When reduced fluid intake is coupled with advancing age, there is a decrease in total body water. Older individuals have impaired renal fluid conservation mechanisms and, as noted above, have impaired responses to heat and cold stress. 33 , 34 All of these factors contribute to an increased risk of hypohydration and dehydration in the elderly.

With regard to physiology, the role of water in health is generally characterized in terms of deviations from an ideal hydrated state, generally in comparison to dehydration. The concept of dehydration encompasses both the process of losing body water and the state of dehydration. Much of the research on water and physical or mental functioning compares a euhydrated state, usually achieved by provision of water sufficient to overcome water loss, to a dehydrated state, which is achieved via withholding of fluids over time and during periods of heat stress or high activity. In general, provision of water is beneficial in individuals with a water deficit, but little research supports the notion that additional water in adequately hydrated individuals confers any benefit.

Physical performance

The role of water and hydration in physical activity, particularly in athletes and in the military, has been of considerable interest and is well-described in the scientific literature. 37 , – 39 During challenging athletic events, it is not uncommon for athletes to lose 6–10% of body weight through sweat, thus leading to dehydration if fluids have not been replenished. However, decrements in the physical performance of athletes have been observed under much lower levels of dehydration, i.e., as little as 2%. 38 Under relatively mild levels of dehydration, individuals engaging in rigorous physical activity will experience decrements in performance related to reduced endurance, increased fatigue, altered thermoregulatory capability, reduced motivation, and increased perceived effort. 40 , 41 Rehydration can reverse these deficits and reduce the oxidative stress induced by exercise and dehydration. 42 Hypohydration appears to have a more significant impact on high-intensity and endurance activity, such as tennis 43 and long-distance running, 44 than on anaerobic activities, 45 such as weight lifting, or on shorter-duration activities, such as rowing. 46

During exercise, individuals may not hydrate adequately when allowed to drink according to thirst. 32 After periods of physical exertion, voluntary fluid intake may be inadequate to offset fluid deficits. 1 Thus, mild-to-moderate dehydration can persist for some hours after the conclusion of physical activity. Research performed on athletes suggests that, principally at the beginning of the training season, they are at particular risk for dehydration due to lack of acclimatization to weather conditions or suddenly increased activity levels. 47 , 48 A number of studies show that performance in temperate and hot climates is affected to a greater degree than performance in cold temperatures. 41 , – 50 Exercise in hot conditions with inadequate fluid replacement is associated with hyperthermia, reduced stroke volume and cardiac output, decreases in blood pressure, and reduced blood flow to muscle. 51

During exercise, children may be at greater risk for voluntary dehydration. Children may not recognize the need to replace lost fluids, and both children as well as coaches need specific guidelines for fluid intake. 52 Additionally, children may require more time to acclimate to increases in environmental temperature than adults. 30 , 31 Recommendations are for child athletes or children in hot climates to begin athletic activities in a well-hydrated state and to drink fluids over and above the thirst threshold.

Cognitive performance

Water, or its lack (dehydration), can influence cognition. Mild levels of dehydration can produce disruptions in mood and cognitive functioning. This may be of special concern in the very young, very old, those in hot climates, and those engaging in vigorous exercise. Mild dehydration produces alterations in a number of important aspects of cognitive function such as concentration, alertness, and short-term memory in children (10–12 y), 32 young adults (18–25 y), 53 , – 56 and the oldest adults (50–82 y). 57 As with physical functioning, mild-to-moderate levels of dehydration can impair performance on tasks such as short-term memory, perceptual discrimination, arithmetic ability, visuomotor tracking, and psychomotor skills. 53 , – 56 However, mild dehydration does not appear to alter cognitive functioning in a consistent manner. 53 , – 58 In some cases, cognitive performance was not significantly affected in ranges from 2% to 2.6% dehydration. 56 , 58 Comparing across studies, performance on similar cognitive tests was divergent under dehydration conditions. 54 , 56 In studies conducted by Cian et al., 53 , 54 participants were dehydrated to approximately 2.8% either through heat exposure or treadmill exercise. In both studies, performance was impaired on tasks examining visual perception, short-term memory, and psychomotor ability. In a series of studies using exercise in conjunction with water restriction as a means of producing dehydration, D'Anci et al. 56 observed only mild decrements in cognitive performance in healthy young men and women athletes. In these experiments, the only consistent effect of mild dehydration was significant elevations of subjective mood score, including fatigue, confusion, anger, and vigor. Finally, in a study using water deprivation alone over a 24-h period, no significant decreases in cognitive performance were seen with 2.6% dehydration. 58 It is therefore possible that heat stress may play a critical role in the effects of dehydration on cognitive performance.

Reintroduction of fluids under conditions of mild dehydration can reasonably be expected to reverse dehydration-induced cognitive deficits. Few studies have examined how fluid reintroduction may alleviate the negative effects of dehydration on cognitive performance and mood. One study 59 examined how water ingestion affected arousal and cognitive performance in young people following a period of 12-h water restriction. While cognitive performance was not affected by either water restriction or water consumption, water ingestion affected self-reported arousal. Participants reported increased alertness as a function of water intake. Rogers et al. 60 observed a similar increase in alertness following water ingestion in both high- and low-thirst participants. Water ingestion, however, had opposite effects on cognitive performance as a function of thirst. High-thirst participants' performance on a cognitively demanding task improved following water ingestion, but low-thirst participants' performance declined. In summary, hydration status consistently affected self-reported alertness, but effects on cognition were less consistent.

Several recent studies have examined the utility of providing water to school children on attentiveness and cognitive functioning in children. 61 , – 63 In these experiments, children were not fluid restricted prior to cognitive testing, but were allowed to drink as usual. Children were then provided with a drink or no drink 20–45 min before the cognitive test sessions. In the absence of fluid restriction and without physiological measures of hydration status, the children in these studies should not be classified as dehydrated. Subjective measures of thirst were reduced in children given water, 62 and voluntary water intake in children varied from 57 mL to 250 mL. In these studies, as in the studies in adults, the findings were divergent and relatively modest. In the research led by Edmonds et al., 61 , 62 children in the groups given water showed improvements in visual attention. However, effects on visual memory were less consistent, with one study showing no effects of drinking water on a spot-the-difference task in 6–7-year-old children 61 and the other showing a significant improvement in a similar task in 7–9-year-old children. 62 In the research described by Benton and Burgess, 63 memory performance was improved by provision of water but sustained attention was not altered with provision of water in the same children.

Taken together, these studies indicate that low-to-moderate dehydration may alter cognitive performance. Rather than indicating that the effects of hydration or water ingestion on cognition are contradictory, many of the studies differ significantly in methodology and in measurement of cognitive behaviors. These variances in methodology underscore the importance of consistency when examining relatively subtle chances in overall cognitive performance. However, in those studies in which dehydration was induced, most combined heat and exercise; this makes it difficult to disentangle the effects of dehydration on cognitive performance in temperate conditions from the effects of heat and exercise. Additionally, relatively little is known about the mechanism of mild dehydration's effects on mental performance. It has been proposed that mild dehydration acts as a physiological stressor that competes with and draws attention from cognitive processes. 64 However, research on this hypothesis is limited and merits further exploration.

Dehydration and delirium

Dehydration is a risk factor for delirium and for delirium presenting as dementia in the elderly and in the very ill. 65 , – 67 Recent work shows that dehydration is one of several predisposing factors for confusion observed in long-term-care residents 67 ; however, in this study, daily water intake was used as a proxy measure for dehydration rather than other, more direct clinical assessments such as urine or plasma osmolality. Older people have been reported as having reduced thirst and hypodipsia relative to younger people. In addition, fluid intake and maintenance of water balance can be complicated by factors such as disease, dementia, incontinence, renal insufficiency, restricted mobility, and drug side effects. In response to primary dehydration, older people have less thirst sensation and reduced fluid intakes in comparison to younger people. However, in response to heat stress, while older people still display a reduced thirst threshold, they do ingest comparable amounts of fluid to younger people. 20

Gastrointestinal function

Fluids in the diet are generally absorbed in the proximal small intestine, and the absorption rate is determined by the rate of gastric emptying to the small intestine. Therefore, the total volume of fluid consumed will eventually be reflected in water balance, but the rate at which rehydration occurs is dependent upon factors affecting the rate of delivery of fluids to the intestinal mucosa. The gastric emptying rate is generally accelerated by the total volume consumed and slowed by higher energy density and osmolality. 68 In addition to water consumed in food (1 L/day) and beverages (circa 2–3 L/day), digestive secretions account for a far greater portion of water that passes through and is absorbed by the gastrointestinal tract (circa 8 L/day). 69 The majority of this water is absorbed by the small intestine, with a capacity of up to 15 L/day with the colon absorbing some 5 L/day. 69

Constipation, characterized by slow gastrointestinal transit, small, hard stools, and difficulty in passing stool, has a number of causes, including medication use, inadequate fiber intake, poor diet, and illness. 70 Inadequate fluid consumption is touted as a common culprit in constipation, and increasing fluid intake is a frequently recommended treatment. Evidence suggests, however, that increasing fluids is only useful to individuals in a hypohydrated state, and is of little utility in euhydrated individuals. 70 In young children with chronic constipation, increasing daily water intake by 50% did not affect constipation scores. 71 For Japanese women with low fiber intake, concomitant low water intake in the diet is associated with increased prevalence of constipation. 72 In older individuals, low fluid intake is a predictor for increased levels of acute constipation, 73 , 74 with those consuming the least amount of fluid having over twice the frequency of constipation episodes than those consuming the most fluid. In one trial, researchers compared the utility of carbonated mineral water in reducing functional dyspepsia and constipation scores to tap water in individuals with functional dyspepsia. 75 When comparing carbonated mineral water to tap water, participants reported improvements in subjective gastric symptoms, but there were no significant improvements in gastric or intestinal function. The authors indicate it is not possible to determine to what degree the mineral content of the two waters contributed to perceived symptom relief, as the mineral water contained greater levels of magnesium and calcium than the tap water. The available evidence suggests that increased fluid intake should only be indicated in individuals in a hypohydrated state. 69 , 71

Significant water loss can occur through the gastrointestinal tract, and this can be of great concern in the very young. In developing countries, diarrheal diseases are a leading cause of death in children, resulting in approximately 1.5–2.5 million deaths per year. 76 Diarrheal illness results not only in a reduction in body water, but also in potentially lethal electrolyte imbalances. Mortality in such cases can many times be prevented with appropriate oral rehydration therapy, by which simple dilute solutions of salt and sugar in water can replace fluid lost by diarrhea. Many consider application of oral rehydration therapy to be one of the significant public health developments of the last century. 77

Kidney function

As noted above, the kidney is crucial in regulating water balance and blood pressure as well as removing waste from the body. Water metabolism by the kidney can be classified into regulated and obligate. Water regulation is hormonally mediated, with the goal of maintaining a tight range of plasma osmolality (between 275 and 290 mOsm/kg). Increases in plasma osmolality and activation of osmoreceptors (intracellular) and baroreceptors (extracellular) stimulate hypothalamic release of arginine vasopressin (AVP). AVP acts at the kidney to decrease urine volume and promote retention of water, and the urine becomes hypertonic. With decreased plasma osmolality, vasopressin release is inhibited, and the kidney increases hypotonic urinary output.

In addition to regulating fluid balance, the kidneys require water for the filtration of waste from the bloodstream and excretion via urine. Water excretion via the kidney removes solutes from the blood, and a minimum obligate urine volume is required to remove the solute load with a maximum output volume of 1 L/h. 78 This obligate volume is not fixed, but is dependent upon the amount of metabolic solutes to be excreted and levels of AVP. Depending on the need for water conservation, basal urine osmolality ranges from 40 mOsm/kg to a maximum of 1,400 mOsm/kg. 78 The ability to both concentrate and dilute urine decreases with age, with a lower value of 92 mOsm/kg and an upper range falling between 500 and 700 mOsm/kg for individuals over the age of 70 years. 79 , – 81 Under typical conditions, in an average adult, urine volume of 1.5 to 2.0 L/day would be sufficient to clear a solute load of 900 to 1,200 mOsm/day. During water conservation and the presence of AVP, this obligate volume can decrease to 0.75–1.0 L/day and during maximal diuresis up to 20 L/day can be required to remove the same solute load. 78 , – 81 In cases of water loading, if the volume of water ingested cannot be compensated for with urine output, having overloaded the kidney's maximal output rate, an individual can enter a hyponatremic state.

Heart function and hemodynamic response

Blood volume, blood pressure, and heart rate are closely linked. Blood volume is normally tightly regulated by matching water intake and water output, as described in the section on kidney function. In healthy individuals, slight changes in heart rate and vasoconstriction act to balance the effect of normal fluctuations in blood volume on blood pressure. 82 Decreases in blood volume can occur, through blood loss (or blood donation), or loss of body water through sweat, as seen with exercise. Blood volume is distributed differently relative to the position of the heart, whether supine or upright, and moving from one position to the other can lead to increased heart rate, a fall in blood pressure, and, in some cases, syncope. This postural hypotension (or orthostatic hypotension) can be mediated by drinking 300–500 mL of water. 83 , 84 Water intake acutely reduces heart rate and increases blood pressure in both normotensive and hypertensive individuals. 85 These effects of water intake on the pressor effect and heart rate occur within 15–20 min of drinking water and can last for up to 60 min. Water ingestion is also beneficial in preventing vasovagal reaction with syncope in blood donors at high risk for post-donation syncope. 86 The effect of water intake in these situations is thought to be due to effects on the sympathetic nervous system rather than to changes in blood volume. 83 , 84 Interestingly, in rare cases, individuals may experience bradycardia and syncope after swallowing cold liquids. 87 , – 89 While swallow syncope can be seen with substances other than water, swallow syncope further supports the notion that the result of water ingestion in the pressor effect has both a neural component as well as a cardiac component.

Water deprivation and dehydration can lead to the development of headache. 90 Although this observation is largely unexplored in the medical literature, some observational studies indicate that water deprivation, in addition to impairing concentration and increasing irritability, can serve as a trigger for migraine and can also prolong migraine. 91 , 92 In those with water deprivation-induced headache, ingestion of water provided relief from headache in most individuals within 30 min to 3 h. 92 It is proposed that water deprivation-induced headache is the result of intracranial dehydration and total plasma volume. Although provision of water may be useful in relieving dehydration-related headache, the utility of increasing water intake for the prevention of headache is less well documented.

The folk wisdom that drinking water can stave off headaches has been relatively unchallenged, and has more traction in the popular press than in the medical literature. Recently, one study examined increased water intake and headache symptoms in headache patients. 93 In this randomized trial, patients with a history of different types of headache, including migraine and tension headache, were either assigned to a placebo condition (a nondrug tablet) or the increased water condition. In the water condition, participants were instructed to consume an additional volume of 1.5 L water/day on top of what they already consumed in foods and fluids. Water intake did not affect the number of headache episodes, but it was modestly associated with reduction in headache intensity and reduced duration of headache. The data from this study suggest that the utility of water as prophylaxis is limited in headache sufferers, and the ability of water to reduce or prevent headache in the broader population remains unknown.

One of the more pervasive myths regarding water intake is its relation to improvements of the skin or complexion. By improvement, it is generally understood that individuals are seeking to have a more “moisturized” look to the surface skin, or to minimize acne or other skin conditions. Numerous lay sources such as beauty and health magazines as well as postings on the Internet suggest that drinking 8–10 glasses of water a day will “flush toxins from the skin” and “give a glowing complexion” despite a general lack of evidence 94 , 95 to support these proposals. The skin, however, is important for maintaining body water levels and preventing water loss into the environment.

The skin contains approximately 30% water, which contributes to plumpness, elasticity, and resiliency. The overlapping cellular structure of the stratum corneum and lipid content of the skin serves as “waterproofing” for the body. 96 Loss of water through sweat is not indiscriminate across the total surface of the skin, but is carried out by eccrine sweat glands, which are evenly distributed over most of the body surface. 97 Skin dryness is usually associated with exposure to dry air, prolonged contact with hot water and scrubbing with soap (both strip oils from the skin), medical conditions, and medications. While more serious levels of dehydration can be reflected in reduced skin turgor, 98 , 99 with tenting of the skin acting as a flag for dehydration, overt skin turgor in individuals with adequate hydration is not altered. Water intake, particularly in individuals with low initial water intake, can improve skin thickness and density as measured by sonogram, 100 offsets transepidermal water loss, and can improve skin hydration. 101 Adequate skin hydration, however, is not sufficient to prevent wrinkles or other signs of aging, which are related to genetics and to sun and environmental damage. Of more utility to individuals already consuming adequate fluids is the use of topical emollients; these will improve skin barrier function and improve the look and feel of dry skin. 102 , 103

Many chronic diseases have multifactorial origins. In particular, differences in lifestyle and the impact of environment are known to be involved and constitute risk factors that are still being evaluated. Water is quantitatively the most important nutrient. In the past, scientific interest with regard to water metabolism was mainly directed toward the extremes of severe dehydration and water intoxication. There is evidence, however, that mild dehydration may also account for some morbidities. 4 , 104 There is currently no consensus on a “gold standard” for hydration markers, particularly for mild dehydration. As a consequence, the effects of mild dehydration on the development of several disorders and diseases have not been well documented.

There is strong evidence showing that good hydration reduces the risk of urolithiasis (see Table 2 for evidence categories). Less strong evidence links good hydration with reduced incidence of constipation, exercise asthma, hypertonic dehydration in the infant, and hyperglycemia in diabetic ketoacidosis. Good hydration is associated with a reduction in urinary tract infections, hypertension, fatal coronary heart disease, venous thromboembolism, and cerebral infarct, but all these effects need to be confirmed by clinical trials. For other conditions such as bladder or colon cancer, evidence of a preventive effect of maintaining good hydration is not consistent (see Table 3 ).

Categories of evidence used in evaluating the quality of reports.

Data adapted from Manz. 104

Summary of evidence for association of hydration status with chronic diseases.

Categories of evidence: described in Table 2 .

Water consumption, water requirements, and energy intake are linked in fairly complex ways. This is partially because physical activity and energy expenditures affect the need for water but also because a large shift in beverage consumption over the past century or more has led to consumption of a significant proportion of our energy intake from caloric beverages. Nonregulatory beverage intake, as noted earlier, has assumed a much greater role for individuals. 19 This section reviews current patterns of water intake and then refers to a full meta-analysis of the effects of added water on energy intake. This includes adding water to the diet and water replacement for a range of caloric and diet beverages, including sugar-sweetened beverages, juice, milk, and diet beverages. The third component is a discussion of water requirements and suggestions for considering the use of mL water/kcal energy intake as a metric.

Patterns and trends of water consumption

Measurement of total fluid water consumption in free-living individuals is fairly new in focus. As a result, the state of the science is poorly developed, data are most likely fairly incomplete, and adequate validation of the measurement techniques used is not available. Presented here are varying patterns and trends of water intake for the United States over the past three decades followed by a brief review of the work on water intake in Europe.

There is really no existing information to support an assumption that consumption of water alone or beverages containing water affects hydration differentially. 3 , 105 Some epidemiological data suggest water might have different metabolic effects when consumed alone rather than as a component of caffeinated or flavored or sweetened beverages; however, these data are at best suggestive of an issue deserving further exploration. 106 , 107 As shown below, the research of Ershow et al. indicates that beverages not consisting solely of water do contain less than 100% water.

One study in the United States has attempted to examine all the dietary sources of water. 16 , 17 These data are cited in Table 4 as the Ershow study and were based on National Food Consumption Survey food and fluid intake data from 1977–1978. These data are presented in Table 4 for children aged 2–18 years (Panel A) and for adults aged 19 years and older (Panel B). Ershow et al. 16 , 17 spent a great deal of time working out ways to convert USDA dietary data into water intake, including water absorbed during the cooking process, water in food, and all sources of drinking water.

Beverage pattern trends in the United States for children aged 2–18 years and adults aged 19 years and older, (nationally representative).

Note: The data are age and sex adjusted to 1965.

Values stem from the Ershow calculations. 16

These researchers created a number of categories and used a range of factors measured in other studies to estimate the water categories. The water that is found in food, based on food composition table data, was 393 mL for children. The water that was added as a result of cooking (e.g., rice) was 95 mL. Water consumed as a beverage directly as water was 624 mL. The water found in other fluids, as noted, comprised the remainder of the milliliters, with the highest levels in whole-fat milk and juices (506 mL). There is a small discrepancy between the Ershow data regarding total fluid intake measures for these children and the normal USDA figures. That is because the USDA does not remove milk fats and solids, fiber, and other food constituents found in beverages, particularly juice and milk.

A key point illustrated by these nationally representative US data is the enormous variability between survey waves in the amount of water consumed (see Figure 1 , which highlights the large variation in water intake as measured in these surveys). Although water intake by adults and children increased and decreased at the same time, for reasons that cannot be explained, the variation was greater among children than adults. This is partly because the questions the surveys posed varied over time and there was no detailed probing for water intake, because the focus was on obtaining measures of macro- and micronutrients. Dietary survey methods used in the past have focused on obtaining data on foods and beverages containing nutrient and non-nutritive sweeteners but not on water. Related to this are the huge differences between the the USDA surveys and the National Health and Nutrition Examination Survey (NHANES) performed in 1988–1994 and in 1999 and later. In addition, even the NHANES 1999–2002 and 2003–2006 surveys differ greatly. These differences reflect a shift in the mode of questioning with questions on water intake being included as part of a standard 24-h recall rather than as stand-alone questions. Water intake was not even measured in 1965, and a review of the questionnaires and the data reveals clear differences in the way the questions have been asked and the limitations on probes regarding water intake. Essentially, in the past people were asked how much water they consumed in a day and now they are asked for this information as part of a 24-h recall survey. However, unlike for other caloric and diet beverages, there are limited probes for water alone. The results must thus be viewed as crude approximations of total water intake without any strong research to show if they are over- or underestimated. From several studies of water and two ongoing randomized controlled trials performed by us, it is clear that probes that include consideration of all beverages and include water as a separate item result in the provision of more complete data.

Water consumption trends from USDA and NHANES surveys (mL/day/capita), nationally representative. Note: this includes water from fluids only, excluding water in foods. Sources for 1965, 1977–1978, 1989–1991, and 1994–1998, are USDA. Others are NHANES and 2005–2006 is joint USDA and NHANES.

Water consumption data for Europe are collected far more selectively than even the crude water intake questions from NHANES. A recent report from the European Food Safety Agency provides measures of water consumption from a range of studies in Europe. 4 , – 109 Essentially, what these studies show is that total water intake is lower across Europe than in the United States. As with the US data, none are based on long-term, carefully measured or even repeated 24-h recall measures of water intake from food and beverages. In an unpublished examination of water intake in UK adults in 1986–1987 and in 2001–2002, Popkin and Jebb have found that although intake increased by 226 mL/day over this time period, it was still only 1,787 mL/day in the latter period (unpublished data available from BP); this level is far below the 2,793 mL/day recorded in the United States for 2005–2006 or the earlier US figures for comparably aged adults.

A few studies have been performed in the United States and Europe utilizing 24-h urine and serum osmolality measures to determine total water turnover and hydration status. Results of these studies suggest that US adults consume over 2,100 mL of water per day while adults in Europe consume less than half a liter. 4 , 110 Data on total urine collection would appear to be another useful measure for examining total water intake. Of course, few studies aside from the Donald Study of an adolescent cohort in Germany have collected such data on population levels for large samples. 109

Effects of water consumption on overall energy intake

There is an extensive body of literature that focuses on the impact of sugar-sweetened beverages on weight and the risk of obesity, diabetes, and heart disease; however, the perspective of providing more water and its impact on health has not been examined. The literature on water does not address portion sizes; instead, it focuses mainly on water ad libitum or in selected portions compared with other caloric beverages. A detailed meta-analysis of the effects of water intake alone (i.e., adding additional water) and as a replacement for sugar-sweetened beverages, juice, milk, and diet beverages appears elsewhere. 111

In general, the results of this review suggest that water, when consumed in place of sugar-sweetened beverages, juice, and milk, is linked with reduced energy intake. This finding is mainly derived from clinical feeding studies but also from one very good randomized, controlled school intervention and several other epidemiological and intervention studies. Aside from the issue of portion size, factors such as the timing of beverage and meal intake (i.e., the delay between consumption of the beverage and consumption of the meal) and types of caloric sweeteners remain to be considered. However, when beverages are consumed in normal free-living conditions in which five to eight daily eating occasions are the norm, the delay between beverage and meal consumption may matter less. 112 , – 114

The literature on the water intake of children is extremely limited. However, the excellent German school intervention with water suggests the effects of water on the overall energy intake of children might be comparable to that of adults. 115 In this German study, children were educated on the value of water and provided with special filtered drinking fountains and water bottles in school. The intervention schoolchildren increased their water intake by 1.1 glasses/day ( P  < 0.001) and reduced their risk of overweight by 31% (OR = 0.69, P  = 0.40).

Classically, water data are examined in terms of milliliters (or some other measure of water volume consumed per capita per day by age group). This measure does not link fluid intake and caloric intake. Disassociation of fluid and calorie intake is difficult for clinicians dealing with older persons with reduced caloric intake. This milliliter water measure assumes some mean body size (or surface area) and a mean level of physical activity – both of which are determinants of not only energy expenditure but also water balance. Children are dependent on adults for access to water, and studies suggest that their larger surface area to volume ratio makes them susceptible to changes in skin temperatures linked with ambient temperature shifts. 116 One option utilized by some scholars is to explore food and beverage intake in milliliters per kilocalorie (mL/kcal), as was done in the 1989 US recommended dietary allowances. 4 , 117 This is an option that is interpretable for clinicians and which incorporates, in some sense, body size or surface area and activity. Its disadvantage is that water consumed with caloric beverages affects both the numerator and the denominator; however, an alternative measure that could be independent of this direct effect on body weight and/or total caloric intake is not presently known.

Despite its critical importance in health and nutrition, the array of available research that serves as a basis for determining requirements for water or fluid intake, or even rational recommendations for populations, is limited in comparison with most other nutrients. While this deficit may be partly explained by the highly sensitive set of neurophysiological adaptations and adjustments that occur over a large range of fluid intakes to protect body hydration and osmolarity, this deficit remains a challenge for the nutrition and public health community. The latest official effort at recommending water intake for different subpopulations occurred as part of the efforts to establish Dietary Reference Intakes in 2005, as reported by the Institute of Medicine of the National Academies of Science. 3 As a graphic acknowledgment of the limited database upon which to express estimated average requirements for water for different population groups, the Committee and the Institute of Medicine stated: “While it might appear useful to estimate an average requirement (an EAR) for water, an EAR based on data is not possible.” Given the extreme variability in water needs that are not solely based on differences in metabolism, but also on environmental conditions and activities, there is not a single level of water intake that would assure adequate hydration and optimum health for half of all apparently healthy persons in all environmental conditions. Thus, an adequate intake (AI) level was established in place of an EAR for water.

The AIs for different population groups were set as the median water intakes for populations, as reported in the National Health and Nutrition Examination Surveys; however, the intake levels reported in these surveys varied greatly based on the survey years (e.g., NHANES 1988–1994 versus NHANES 1999–2002) and were also much higher than those found in the USDA surveys (e.g., 1989–1991, 1994–1998, or 2005–2006). If the AI for adults, as expressed in Table 5 , is taken as a recommended intake, the wisdom of converting an AI into a recommended water or fluid intake seems questionable. The first problem is the almost certain inaccuracy of the fluid intake information from the national surveys, even though that problem may also exist for other nutrients. More importantly, from the standpoint of translating an AI into a recommended fluid intake for individuals or populations, is the decision that was made when setting the AI to add an additional roughly 20% of water intake, which is derived from some foods in addition to water and beverages. While this may have been a legitimate effort to use total water intake as a basis for setting the AI, the recommendations that derive from the IOM report would be better directed at recommendations for water and other fluid intake on the assumption that the water content of foods would be a “passive” addition to total water intake. In this case, the observations of the dietary reference intake committee that it is necessary for water intake to meet needs imposed by metabolism and environmental conditions must be extended to consider three added factors, namely body size, gender, and physical activity. Those are the well-studied factors that allow a rather precise measurement and determination of energy intake requirements. It is, therefore, logical that those same factors might underlie recommendations to meet water intake needs in the same populations and individuals. Consideration should also be given to the possibility that water intake needs would best be expressed relative to the calorie requirements, as is done regularly in the clinical setting, and data should be gathered to this end through experimental and population research.

Water requirements expressed in relation to energy recommendations.

AI for total fluids derived from dietary reference intakes for water, potassium, sodium, chloride, and sulphate.

Ratios for water intake based on the AI for water in liters/day calculated using EER for each range of physical activity. EER adapted from the Institute of Medicine Dietary Reference Intakes Macronutrients Report, 2002.

It is important to note that only a few countries include water on their list of nutrients. 118 The European Food Safety Authority is developing a standard for all of Europe. 105 At present, only the United States and Germany provide AI values for water. 3 , 119

Another approach to the estimation of water requirements, beyond the limited usefulness of the AI or estimated mean intake, is to express water intake requirements in relation to energy requirements in mL/kcal. An argument for this approach includes the observation that energy requirements for each age and gender group are strongly evidence-based and supported by extensive research taking into account both body size and activity level, which are crucial determinants of energy expenditure that must be met by dietary energy intake. Such measures of expenditure have used highly accurate methods, such as doubly labeled water; thus, estimated energy requirements have been set based on solid data rather than the compromise inherent in the AIs for water. Those same determinants of energy expenditure and recommended intake are also applicable to water utilization and balance, and this provides an argument for pegging water/fluid intake recommendations to the better-studied energy recommendations. The extent to which water intake and requirements are determined by energy intake and expenditure is understudied, but in the clinical setting it has long been practice to supply 1 mL/kcal administered by tube to patients who are unable to take in food or fluids. Factors such as fever or other drivers of increased metabolism affect both energy expenditure and fluid loss and are thus linked in clinical practice. This concept may well deserve consideration in the setting of population intake goals.

Finally, for decades there has been discussion about expressing nutrient requirements per 1,000 kcal so that a single number would apply reasonably across the spectrum of age groups. This idea, which has never been adopted by the Institute of Medicine and the National Academies of Science, may lend itself to an improved expression of water/fluid intake requirements, which must eventually replace the AIs. Table 5 presents the IOM water requirements and then develops a ratio of mL/kcal based on them. The European Food Safety Agency refers positively to the possibility of expressing water intake recommendations in mL/kcal as a function of energy requirements. 105 Outliers in the adult male categories, which reach ratios as high as 1.5, may well be based on the AI data from the United States, which are above those in the more moderate and likely more accurate European recommendations.

The topic of utilizing mL/kcal to examine water intake and water gaps is explored in Table 6 , which takes the full set of water intake AIs for each age-gender grouping and examines total intake. The data suggest a high level of fluid deficiency. Since a large proportion of fluids in the United States is based on caloric beverages and this proportion has changed markedly over the past 30 years, fluid intake increases both the numerator and the denominator of this mL/kcal relationship. Nevertheless, even using 1 mL/kcal as the AI would leave a gap for all children and adolescents. The NHANES physical activity data were also translated into METS/day to categorize all individuals by physical activity level and thus varying caloric requirements. Use of these measures reveals a fairly large fluid gap, particularly for adult males as well as children ( Table 6 ).

Water intake and water intake gaps based on US Water Adequate Intake Recommendations (based on utilization of water and physical activity data from NHANES 2005–2006).

Note: Recommended water intake for actual activity level is the upper end of the range for moderate and active.

A weighted average for the proportion of individuals in each METS-based activity level.

This review has pointed out a number of issues related to water, hydration, and health. Since water is undoubtedly the most important nutrient and the only one for which an absence will prove lethal within days, understanding of water measurement and water requirements is very important. The effects of water on daily performance and short- and long-term health are quite clear. The existing literature indicates there are few negative effects of water intake while the evidence for positive effects is quite clear.

Little work has been done to measure total fluid intake systematically, and there is no understanding of measurement error and best methods of understanding fluid intake. The most definitive US and European documents on total water requirements are based on these extant intake data. 3 , 105 The absence of validation methods for water consumption intake levels and patterns represents a major gap in knowledge. Even varying the methods of probing in order to collect better water recall data has been little explored.

On the other side of the issue is the need to understand total hydration status. There are presently no acceptable biomarkers of hydration status at the population level, and controversy exists about the current knowledge of hydration status among older Americans. 6 , 120 Thus, while scholars are certainly focused on attempting to create biomarkers for measuring hydration status at the population level, the topic is currently understudied.

As noted, the importance of understanding the role of fluid intake on health has emerged as a topic of increasing interest, partially because of the trend toward rising proportions of fluids being consumed in the form of caloric beverages. The clinical, epidemiological, and intervention literature on the effects of added water on health are covered in a related systematic review. 111 The use of water as a replacement for sugar-sweetened beverages, juice, or whole milk has clear effects in that energy intake is reduced by about 10–13% of total energy intake. However, only a few longer-term systematic interventions have investigated this topic and no randomized, controlled, longer-term trials have been published to date. There is thus very minimal evidence on the effects of just adding water to the diet and of replacing water with diet beverages.

There are many limitations to this review. One certainly is the lack of discussion of potential differences in the metabolic functioning of different types of beverages. 121 Since the literature in this area is sparse, however, there is little basis for delving into it at this point. A discussion of the potential effects of fructose (from all caloric sweeteners when consumed in caloric beverages) on abdominal fat and all of the metabolic conditions directly linked with it (e.g., diabetes) is likewise lacking. 122 , – 125 A further limitation is the lack of detailed review of the array of biomarkers being considered to measure hydration status. Since there is no measurement in the field today that covers more than a very short time period, except for 24-hour total urine collection, such a discussion seems premature.

Some ways to examine water requirements have been suggested in this review as a means to encourage more dialogue on this important topic. Given the significance of water to our health and of caloric beverages to our total energy intake, as well as the potential risks of nutrition-related noncommunicable diseases, understanding both the requirements for water in relation to energy requirements, and the differential effects of water versus other caloric beverages, remain important outstanding issues.

This review has attempted to provide some sense of the importance of water to our health, its role in relationship to the rapidly increasing rates of obesity and other related diseases, and the gaps in present understanding of hydration measurement and requirements. Water is essential to our survival. By highlighting its critical role, it is hoped that the focus on water in human health will sharpen.

The authors wish to thank Ms. Frances L. Dancy for administrative assistance, Mr. Tom Swasey for graphics support, Dr. Melissa Daniels for assistance, and Florence Constant (Nestle's Water Research) for advice and references.

This work was supported by the Nestlé Waters, Issy-les-Moulineaux, France, 5ROI AGI0436 from the National Institute on Aging Physical Frailty Program, and NIH R01-CA109831 and R01-CA121152.

Declaration of interest

The authors have no relevant interests to declare.

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• dehydration
• energy intake
• water drinking
• fluid intake
• water requirements

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Open Access

Peer-reviewed

Research Article

Bottled water, tap water and household-treated tap water–insight into potential health risks and aesthetic concerns in drinking water

Roles Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Supervision, Validation, Writing – original draft

Affiliation SimpleLab, Inc. Berkeley, California, United States of America

Roles Data curation, Investigation, Writing – review & editing

Affiliations SimpleLab, Inc. Berkeley, California, United States of America, Department of Neurosciences, Case Western Reserve University, Cleveland, Ohio, United States of America

Roles Formal analysis, Visualization, Writing – review & editing

Roles Conceptualization, Formal analysis, Funding acquisition, Methodology, Project administration, Supervision, Writing – original draft

* E-mail: [email protected]

• Samantha E. Bear, 
• Talya Waxenberg, 
• Charles R. Schroeder, 
• Jessica J. Goddard

• Published: September 4, 2024
• https://doi.org/10.1371/journal.pwat.0000272
• Reader Comments

Understanding drinking water quality at the point-of-use across a range of consumer options is essential for designing effective public health interventions in the face of deteriorating source waters and complex contaminant mixtures. This is especially pressing as the popularity of tap water alternatives like bottled water and household treatment increases, yet this data is largely missing from the academic literature and policy discussions. This study presents one of the first evaluations of water quality comparing three common consumer drinking water options in the nine county San Francisco Bay Area with a survey of 100 analytes in 100 bottled water samples, 603 tap water samples, and 111 samples of household-treated tap water. Analytes measured included general water quality characteristics, metals, other inorganics, volatile organic compounds (including disinfection byproducts), and three microbial indicator species in bottled water only. Samples were evaluated to assess potential taste, odor, and color issues, as well as potential health risks by calculating cumulative toxicity quotients to reflect the additive toxicity of chemical mixtures. All three drinking water options had potential health risks, primarily driven by the presence of trihalomethanes (contributing from 76.7 to 94.5% of the total cumulative toxicity across the three drinking water options). While tap water had the highest potential toxicity among the three drinking water options, results suggest that household-scale treatment may reduce the potential for aesthetic issues and health risks of tap water.

Citation: Bear SE, Waxenberg T, Schroeder CR, Goddard JJ (2024) Bottled water, tap water and household-treated tap water–insight into potential health risks and aesthetic concerns in drinking water. PLOS Water 3(9): e0000272. https://doi.org/10.1371/journal.pwat.0000272

Editor: Inderjeet Tyagi, ZSI: Zoological Survey of India, INDIA

Received: March 5, 2024; Accepted: July 31, 2024; Published: September 4, 2024

Copyright: © 2024 Bear et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All data required to reproduce the results and statistics of this study are provided in the SI or are readily available for download. Individual sample results were de-identified and anonymized and are available in Supporting Information Table S8.

Funding: The authors received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

Abbreviations: BW, bottled water; HTTW, household-treated tap water; TW, tap water; TQ, toxicity quotient; POU, point-of-use; POE, point-of-entry; EPA, Environmental Protection Agency; FDA, Food and Drug Administration; SOQ, Standards of Quality; PET, polyethylene terephthalate; VOC, volatile organic compound; DBP, disinfection byproduct; THM, trihalomethane

1. Introduction

Tap water quality issues are on the rise in the US. Deteriorating infrastructure [ 1 ], climate change pressures on source waters [ 2 , 3 ], increasingly complex chemical mixtures in the environment [ 4 , 5 ], governance failures [ 6 ], and low technical, financial and managerial capacity have led to compounding pressures on water systems. Lead, arsenic, nitrate, uranium and bacterial contaminants are all federally regulated and frequently found in violation of drinking water standards across the US [ 7 – 9 ]. Where tap water quality is in question or consumers distrust their water system for other reasons, people turn to alternative sources like bottled water [ 10 ] and household-scale treatment of their tap water [ 11 – 13 ]. Bottled water use is growing rapidly, with per capita consumption in the US having increased from 27.8 gallons per person per year in 2010 to 45.2 gallons per person per year in 2020 [ 14 ]. Household water treatment is a 2.09-billion-dollar market in the US [ 15 ]. While these alternatives to tap water are attracting a growing share of tap water consumers, insight into their water quality implications is scant. Lack of adequate monitoring data across consumer options hinders policymakers’ ability to identify effective economic and public health interventions to address tap water quality issues and public health more broadly. This study offers a comparative analysis of bottled water, household-treated tap water, and tap water quality using a unique dataset to evaluate potential organoleptic and toxicity trade-offs among drinking water options for households in the San Francisco Bay Area. The resulting analysis offers insight into multiple toxicity mitigation priorities for improving drinking water quality.

There is a widespread perception that bottled water is “pure” and free of contaminants, due in part to misleading marketing [ 16 – 18 ]. Additionally, aesthetic properties of tap water like taste and odor have been documented to impact people’s perception of tap water safety [ 19 – 21 ], potentially driving people toward alternatives like bottled water [ 22 , 23 ]. However, a wide range of contaminants have been identified in US bottled water due to contamination from source water, bottle processing, or packaging material leachate [ 16 ]. Contaminants detected in bottled water products include bacteria, various heavy metals (including lead), volatile and semi-volatile organic contaminants (including phthalates), disinfection byproducts, radiological elements, microplastics, and various PFAS compounds [ 24 – 31 ].

Households seeking improved tap water also turn to point-of-entry (POE) and point-of-use (POU) treatment of delivered tap water. In the international context, concerns about appropriate technology selection and whether systems are maintained appropriately are central to understanding household-treated tap water quality [ 32 ]. In the US, household behaviors with treatment equipment and their impact on water quality are unknown. Evidence suggests that people purchase treatment units in response to publicized water quality contamination events or concerns about the taste, odor and color of their water [ 23 ], rather than in response to targeted testing to characterize on-site contamination. While perceptions can correlate with contaminant occurrence, there are many contamination issues that have no organoleptic effects. As such, household-treated tap water poses an exposure risk if treatment is not tailored to a household’s water quality.

The existing literature on drinking water quality is not typically geared toward understanding differences among drinking water options at the household level primarily due to a lack of adequate data. Monitoring and reporting for water system-supplied tap water quality is limited due to a focus on regulated contaminants that are not monitored at the tap (except for lead). Previous studies of tap water quality have been extensive in the contaminants they evaluate but have smaller sample sizes (≤45) [ 4 , 33 – 35 ]. In a study of public tap water and private well supplies in North and South Dakota, the authors concluded that public monitoring data beyond water system compliance is needed “to inform consumer POE/POU treatment decisions’’ across the US [ 35 ]. However, while household-treated tap water quality has been studied internationally [ 36 ], to our knowledge, there are no large-scale studies of household-treated tap water in the US. Also, while numerous bottled water quality analyses exist, they rarely represent the quality of a “typical” bottled water purchase based on the market share of products in a given region. Thus, while these studies indicate potential contamination across the different water sources, a comparative picture of water quality across these three consumer options is lacking.

To our knowledge, this study is one of the first large sample size water quality comparisons among consumer drinking water options and the first U.S. based study of household-treated tap water. One hundred bottled water products (across 89 brands) were collected and tested, and this data was compared to 714 tap water samples across the San Francisco Bay Area collected by households using a consumer test kit product–including 603 direct tap water samples and 111 samples with follow-up household water treatment. The bottled water sample set reflects a “typical” bottled water purchase in the Bay Area, whereas the 714 tap water samples are part of a citizen-science dataset (a convenience sample). One hundred analytes, spanning metals, volatile organic compounds, and common water quality parameters, were surveyed in all three sources, as well as three bacteriological indicators in bottled water.

Potential risks to human health were evaluated using a cumulative toxicity framework in which the concentrations of analytes in a sample were compared to health benchmarks, and potential organoleptic effects were also identified via comparison with aesthetic benchmarks [ 37 , 38 ]. The findings highlight potential drivers of water source preference with respect to organoleptics, as well as drivers of cumulative toxicity, for all three drinking water options. Tractable recommendations are offered for consumers and policymakers aspiring to improve POU tap water quality in the face of complex environmental and financial trade-offs among drinking water options.

To compare the quality of drinking water options in the Bay Area, this study leverages a primary dataset of bottled water samples and a unique secondary dataset of (unpaired) tap water samples and household-treated tap water samples. Each sample was evaluated for 100 analytes, many with possible organoleptic effects and/or potential toxicity. A dataset of aesthetic and health benchmarks for drinking water analytes was compiled from engineering, toxicology, and public health literature to identify concentrations of concern. These data were combined to analyze levels of exceedance and potential toxicity across all three drinking water options. This section first presents the methods of sample collection and laboratory analysis used in each dataset, followed by the comparative data analysis approach.

2.1. Bottled water sample selection and collection

A sample design was developed to represent a “typical” bottled water (BW) purchase for consumers in the San Francisco Bay Area nine county region (Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma counties). A representative sample set was considered to be one that approximately mimicked the market share of BW products sold in the US in 2020 by Food and Drug Administration (FDA) category [ 39 ]. FDA categories are based on the source water and/or water treatment used and include “spring water”, “artesian water”, “mineral water”, “well water” and “purified water” [ 40 ]; see Table A in S1 File for sample details. The final sample included 100 BW products encompassing 89 brands (Table A in S1 File ) purchased from 80 stores across the nine-county region (Fig A in S1 File ). Forty six percent of products were from groundwater sources with no specific treatment requirements from FDA, while another 46% of products were from various sources (often unspecified) with FDA treatment requirements (referred to as “purified”, including those marketed as “distilled”). The remaining 8% of products did not meet FDA requirements for any official bottled water categories.

All 100 products were purchased between July 12 th and July 28 th , 2022. They were sent, unopened, to the Microbac Laboratories facility in Dayville, CT for sampling and analysis within one week of purchase.

2.2. Tap water and household-treated tap water sample selection and collection

Tap water and household-treated tap water samples were selected from a secondary data set obtained from SimpleLab, Inc of individual samples taken over time (as opposed to repeat samples at specific locations). All samples in this dataset were from water system supplied households in the nine county San Francisco Bay Area that purchased water quality testing kits from Tap Score TM (a product of SimpleLab, Inc.) between September 17 th , 2020 and August 16 th , 2022 (Fig B in S1 File ). Selected tap water (TW) and household-treated tap water (HTTW) samples were limited to those with the complete set of 100 analytes analyzed in the BW samples to enable a direct comparison. Samples were categorized as HTTW if residents reported using in-home water treatment devices (excluding water softeners), and as TW if not. HTTW samples and TW samples are not paired samples and therefore contaminant removal efficiencies of household treatment choices could not be calculated. The final dataset includes 714 samples: 603 TW samples and 111 HTTW samples. Seventy-seven percent of water systems supplying the TW and HTTW samples in this study rely on surface water as the primary water source, though nearly all have some groundwater-reliant facilities (see Table F in S1 File for summary of water system treatment and water source characteristics).

For sample collection, Tap Score TM test kits included sample containers and detailed instructions regarding appropriate sampling technique. Two sample containers were provided: one 250 mL HDPE bottle for a first draw sample filled to the shoulder (for analysis of general chemical characteristics, metals and other inorganics), and one 40 mL clear glass VOA vial containing 25 mg of ascorbic acid for a fully flushed sample with no headspace (for volatile organic compound analysis).

2.3. Laboratory analyses

All samples across the two datasets were analyzed at accredited, commercial laboratories using EPA-approved methods for 100 select analytes, including general water quality characteristics (e.g., pH, hardness, total dissolved solids, etc.) and chemical constituents (Tables B and C in S1 File ). Analytes were selected based on the contaminants most frequently tested among households that used Tap Score TM . BW was further analyzed for three microbiological indicators (total coliform, E . coli , and total HPC); these indicators were not measured in TW or HTTW samples as they are not included in the standard water testing package. Only quantitative data (> method reporting limits) was reported and considered a detection.

2.4. Data analysis

Sample results were assessed individually for potential toxicity and aesthetic concerns, as well as cumulatively within samples and across drinking water options. Anonymized analytical sample results are provided in Table J in S1 File .

2.4.1. Health and aesthetic benchmarks.

To evaluate potential health risks and organoleptic impacts from the analytes measured, a list of health and aesthetic benchmark values was developed for each analyte. If an analyte has no known impact on human health and/or the aesthetic experience of drinking water, or research is insufficient for determining an impact, no benchmark was assigned.

Health benchmarks were aggregated from various public health agencies and governmental bodies. These benchmarks reflect concentrations of contaminants below which no known non-cancer impacts are expected over a lifetime of exposure (typically toxicity to specific organ systems), or concentrations that result in specific cancer risk levels over a lifetime of exposure (from 10 −4 to 10 −6 ). Similar to previous studies, the lowest health benchmark available for each analyte was used in order to evaluate all analytes against the most health-protective value available [ 24 , 33 – 35 , 37 , 38 , 41 ] (Table D in S1 File ).

Similarly, aesthetic benchmarks were derived by creating a database of benchmark concentrations for analytes that have been associated with organoleptic effects like off tastes or odors, or discoloration, and the lowest concentration among benchmarks was selected as the aesthetic benchmark. These benchmarks were gathered from institutional, governmental and academic sources (Table E in S1 File ).

2.4.2. Cumulative toxicity quotient calculations.

Frameworks for cumulative health impacts assume health risks from exposures are additive and they guide many public health assessments of drinking water quality [ 42 – 44 ]. Without information on duration of exposure, volume of water consumed, or personal susceptibility, health risks or effects cannot be fully characterized. Instead, detected concentrations were compared to benchmarks that indicate potential toxicity of an exposure given (typically) lifetime exposure duration and common assumptions about relative source contributions across exposure pathways. The resultant ratio is known as a toxicity quotient ( TQ ).

2.4.3. Statistical analyses.

Welch’s one-way analysis of variance (ANOVA) was conducted using the rstatix package in R to evaluate difference of means among ∑ TQs in the three sample groups [ 47 , 48 ]. Welch’s test accounts for unbalanced groups and unequal variances among groups. Because means can be sensitive to outliers, a sensitivity analysis was performed removing outliers defined as ∑ TQs greater than 75 th percentile plus 1.5 times the interquartile range for all three sample groups. The null hypothesis was that there was no significant difference in mean ∑ TQs among the three sample groups. Where Welch’s ANOVA was significant, it was followed up with nonparametric Games-Howell posthoc tests to evaluate differences in means among the three sample groups.

3. Results and discussion

A wide variety of contaminants were detected in samples from all three drinking water options, including many with the potential to impact human health or the odor, taste, or color of drinking water. The presence of contaminant mixtures in these samples is consistent with previous studies of BW [ 24 , 30 ] and TW quality in California [ 9 , 49 – 51 ]. Contaminant level summary statistics by drinking water option are shown in Table G in S1 File .

3.1 Exposure-benchmark comparison: Aesthetic benchmarks

Potential aesthetic issues were identified in samples from all three drinking water options, but higher concentrations of contaminants with aesthetic benchmarks were detected in TW and HTTW compared with BW. Forty-one of the 100 analytes measured have aesthetic benchmarks. Twenty of these 41 analytes were detected in at least one sample, including volatile organic compounds (VOCs), metals, other inorganics, and general water quality characteristics such as hardness and total dissolved solids ( Fig 1 ).

• PPT PowerPoint slide
• PNG larger image
• TIFF original image

Detected concentrations (in μg/L) of analytes with aesthetic benchmarks in bottled water (blue, n = 100), household-treated tap water (green, n = 111) and tap water (purple, n = 603) for contaminants that were detected in more than one water source (a) and those detected in only one water source (b). Percent of samples in which analyte was detected on the right. Concentrations are plotted on a log-scale to allow for legibility in comparing concentrations among BW, TW, and HTTW.

https://doi.org/10.1371/journal.pwat.0000272.g001

Across BW samples, six analytes exceeded their aesthetic benchmarks, as compared with eight and 12 in HTTW and TW samples, respectively (Fig C in S1 File ). At least one aesthetic benchmark exceedance was found in 24% (n = 24/100), 44% (n = 49/111), and 41% (n = 246/603) of BW, HTTW, and TW samples, respectively. The concentrations of analytes were generally similar among water sources, with some exceptions where BW concentrations were lower (including zinc, copper, fluoride, and bromoform).

Calcium was the only analyte to exceed aesthetic benchmarks at a higher proportion in BW than in HTTW and TW (4% of results in exceedance in BW versus 0% for both HTTW and TW). Aesthetic exceedances across water sources were largely from analytes that impact taste and staining–such as metals (aluminum, copper, iron, manganese and, for TW only, zinc), magnesium, and sodium (Fig C in S1 File ). For example, magnesium and sodium exceeded taste thresholds for bitter or salty flavors in all water sources. The benchmark for magnesium was exceeded in 16% (n = 16/100), 33% (n = 37/111) and 29% (n = 173/603) of BW, HTTW and TW samples, respectively, and the aesthetic benchmark for sodium was exceeded in 10% (n = 10/100), 19% (n = 21/111) and 20% (n = 122/603) of BW, HTTW and TW samples, respectively. These elements are naturally occurring, likely present in all sources due to natural processes, and are not fully removed via many at-home treatment processes–sodium, in fact, may be added to water that is softened via an ion exchange water softener [ 52 , 53 ].

Iron and copper both exceeded taste thresholds in TW and HTTW in higher proportions than in BW. The aesthetic benchmark for iron was exceeded in 2% (n = 2/100), 4% (n = 4/111) and 10% (n = 62/603) of BW, HTTW and TW samples, respectively, and that of copper was exceeded in 0%, 7% (n = 8/111) and 5% (n = 30/603) of BW, HTTW and TW samples, respectively. These metals can enter drinking water via water distribution lines and household plumbing and fixtures [ 54 , 55 ], all of which BW mostly avoids. These results are consistent with studies showing that aesthetic impacts like off-tastes are common in TW and a primary reason people turn to BW [ 19 – 21 ].

3.2 Exposure-benchmark comparison: Health benchmarks

Analytes with potential health risks were detected in samples from all three drinking water options in exceedance of health benchmarks. Eighty-four of the 100 contaminants tested in all samples have health benchmarks. Forty of these 84 contaminants, including disinfection byproducts, other VOCs, metals, and other inorganics, were detected in at least one sample ( Fig 2 ). Seventeen health benchmarks were exceeded in both BW and HTTW, and 25 were exceeded in TW (Fig D in S1 File ). At least one health benchmark was exceeded in 53% (n = 53/100), 61% (68/111), and 98% (n = 590/603) of BW, HTTW, and TW samples, respectively. These differences likely stem, in large part, from treatment and source water effects across samples.

Detected concentrations (in μg/L) of analytes with health benchmarks in bottled water (blue, n = 100), household-treated tap water (green, n = 111) and tap water (purple, n = 603) for contaminants that were detected in more than one water source (a) and those detected in only one water source (b). For panel (b), one very high value for tin obscures the concentrations of other contaminants and therefore an axis break is plotted showing observations between 0 μg/L and 100 μg/L, and then the very high value at 5,110 μg/L. Percent of samples in which analyte was detected are indicated on the right. Concentrations are plotted on a log-scale to allow for legibility in comparing concentrations among BW, TW, and HTTW.

https://doi.org/10.1371/journal.pwat.0000272.g002

Fewer health benchmark exceedances in BW likely reflects both the high degree of treatment of the 46 purified products (44 of which employed either distillation or reverse osmosis, see Table A in S1 File ) and the overall high integrity of source waters for the 46 groundwater-sourced products. Specific treatment is not required by the FDA for groundwater-sourced BW products as long as they meet quality standards [ 40 ]; only 11 of 46 groundwater-sourced BW products listed any treatment, which included filtration and disinfection (either via UV or ozone). On the other hand, nearly all TW and HTTW samples in this study were taken from water systems that rely on conventional drinking water treatment (coagulation, flocculation, sedimentation, filtration, and disinfection) (Table F in S1 File ). Conventional treatment is largely adequate to meet regulatory standards, but not necessarily effective in reducing contaminant concentrations below health benchmarks or removing them entirely.

While 98% of TW samples had at least one health benchmark exceedance, 61% of HTTW samples had an exceedance, indicating that some treatment effect is likely. Specific treatment information for HTTW samples is not comprehensive in the dataset, but 88 out of 111 samples reported using carbon-based filters and/or reverse osmosis systems, which likely contributed to the lower overall exceedances. However, the proportion of health benchmark exceedances remaining in HTTW samples indicates that barriers still persist for achieving health risk reduction using at-home treatment. For example, household treatment technologies are often purchased in the absence of water testing to identify appropriate technologies, and effective contaminant removal can be hindered by technology selection and improper maintenance.

3.2.1 Trihalomethanes.

The trihalomethanes (THMs) chloroform, bromodichloromethane and dibromochloromethane were three of the contaminants with the most frequent health benchmark exceedances across all samples tested (Fig D in S1 File ). THMs are formed when chlorine disinfectant reacts with natural organic matter in source waters, which is why mitigation strategies employed by water utilities largely focus on controlling precursors to THMs (i.e. monitoring total organic carbon) [ 56 ]. The proportion of samples with THM exceedances was highest in TW, followed by BW and HTTW. There has been growing concern about disinfection byproducts (DBPs) in drinking water [ 57 – 59 ], which is consistent with the detections of these chlorinated DBPs. Health effects of the three THMs include developmental/reproductive effects, liver toxicity, and an increased risk of cancer [ 60 – 63 ]. THMs were the only contaminants analyzed in this study that exceeded the limits guiding their regulation. Four THMs are regulated as a group called total THMs: chloroform, bromoform, bromodichloromethane and dibromochloromethane. Eight BW samples (8%) exceeded the California BW quality regulatory limit of 10 μg/L for total THMs (which is lower than the FDA’s SOQ of 80 μg/L) [ 64 ], while 13 TW samples (2%) exceeded the federal maximum contaminant level of 80 μg/L [ 65 ]. No HTTW samples exceeded either of these regulatory limits. However, individual THMs exceeded their health protective benchmarks–ranging from 0 to 0.22 μg/L (Table D in S1 File )–in all three drinking water options. For example, chloroform exceeded its health benchmark in 32% of BW samples (n = 32/100), 25% of HTTW samples (n = 28/111) and 89% of TW samples (n = 534/603). Exceedances (equal to detections) in BW were similar to the proportion of detections in Bradley et al. [ 24 ]. Most purified BW products employed reverse osmosis as the primary treatment, which has been shown to incompletely remove THMs [ 66 ]. Because regulatory limits for THMs are so much higher than health benchmarks, it is likely that all drinking water options will continue to present health risk while remaining in compliance with regulations.

The high proportion of THM detections in TW is consistent with violation trends in California [ 49 ] and reported concentrations in Bay Area water systems [ 51 ]. Surface water typically has higher levels of organic matter (i.e., THM precursors) than groundwater and, as such, water systems primarily reliant on surface water are at higher risk of THM formation when using chlorine as a disinfectant [ 63 ]. The vast majority of TW and HTTW samples (92%) were taken by households in water systems reliant on surface water as their primary source (of these systems, 52% have facilities that also rely on at least one groundwater source). Moreover, 60% of these samples are from households in water systems that use chlorine or chloramine as a disinfectant (Table F in S1 File ). Taken together, the impact of THMs on potential toxicity across water sources is unsurprising and reflects a significant challenge for water systems reliant on surface water and chlorination.

3.2.2 Metals.

Contamination due to metals is another well-known drinking water safety challenge, often caused by corrosion of pipes and fixtures and/or inadequate corrosion control in the presence of corrosive source waters [ 55 , 67 ]. Lead was detected (and exceeded its health benchmark of 0) in samples from all three drinking water options, though only in one BW sample. In contrast, lead was detected in 30% (n = 33/111) of HTTW samples and 51% (n = 306/603) of TW samples. The proportion of detections in BW is lower than that reported by Bradley et al. [ 24 ], who found lead in five out of 30 samples (17%) but had lower method detection limits than this study. Lead is a persistent challenge due to aging infrastructure across the US, and exposure to lead can cause adverse neurological, developmental, learning and behavioral effects, especially in children [ 68 – 70 ]. The higher proportion of exceedances found in HTTW and TW is consistent with the potential for contamination from the distribution system and on-premises plumbing.

Other metals that exceeded health benchmarks have a variety of potential sources, including on-site fixtures and faucets subject to less stringent regulations than lead in pipes (e.g. copper and nickel), and source waters (arsenic, uranium, cadmium, cobalt). Copper and nickel were detected in samples from all drinking water options and exceeded their health benchmarks in 7% to 14% of HTTW and TW samples, but neither exceeded their benchmarks in BW. A number of geogenic elements also exceeded health benchmarks in samples from all drinking water options, consistent with previous studies [ 24 , 35 , 49 , 51 ]. Uranium exceeded its health benchmark in 6% of BW samples (n = 6/100), as compared with 2% in HTTW (n = 2/111) and TW (n = 13/603). Uranium has been shown to cause kidney and osteo- toxicity in human and animal studies, as well as adverse female reproductive and developmental effects in animal studies [ 71 , 72 ]. Arsenic was detected in a similar proportion of samples in BW and HTTW samples (7% or n = 7/100, and 8% or n = 9/111, respectively), and in a lower proportion of TW samples (3% or n = 16/603). Exposure to arsenic in drinking water has been shown to increase the risk of cancer, as well as cause adverse dermal and blood system impacts [ 73 , 74 ].

Source water is likely the primary driver of these geogenic exceedances. All uranium detections in BW were in groundwater-sourced products (13% of groundwater-sourced BW products; n = 6/46). Similarly, arsenic exceeded its health benchmark in groundwater-sourced BW products only (15%, n = 7/46). Bradley et al. [ 24 ] similarly found uranium and arsenic in groundwater-sourced BW, but at substantially higher proportions (74% and 87% for uranium and arsenic, respectively) using lower detection limits. The lower proportion of these contaminants in HTTW and TW is consistent with the fact that the majority of tap water samples were sourced from surface water, with a smaller proportion of facilities reliant on groundwater sources (Table F in S1 File ).

3.2.3 Other VOCs.

In BW, additional detections and exceedances suggest that bottle production and processing may play a role in water quality. Two petroleum-derived compounds–benzene and toluene were detected in BW only. One benzene detection was in exceedance of the health benchmark, and all 5 toluene detections were below the health benchmark. One possibility is that these contaminants were introduced to bottled water products during processing [ 75 ].

3.2.4 Bacteria.

The microbiological indicators total coliform, E . coli , and total heterotrophic bacteria (total HPC) were evaluated in BW samples only. While no E . coli or total coliform were found in BW samples, heterotrophic bacteria were detected in 43% of BW samples (Fig E in S1 File ). Heterotrophic bacteria are not considered good indicators of pathogenic bacteria [ 76 ], but total HPC serves as an indicator of overall sterility. These findings corroborate previous studies identifying HPC in BW, which found detections in 30% - 71% of samples [ 24 , 27 ]. While tap water samples are likely to have HPC as well because of its ubiquitous presence in the environment, these findings are particularly interesting in BW because of marketing claims about the purity of BW.

3.3 Cumulative toxicity quotients

A cumulative toxicity quotient (∑ TQ ) was calculated for each sample to assess overall potential toxicity by summing detected contaminant concentrations divided by their health benchmarks. Fig 3 plots cumulative toxicity quotients for samples of each drinking water option in comparison with the benchmark equivalent concentration (∑ TQ = 1).

The red line indicates the benchmark equivalent concentration (∑ TQ = 1). Posthoc test results with p-values adjusted for multiple hypothesis testing shown above boxplots to indicate significant difference in group means between pairs at p <0.0001 (****).

https://doi.org/10.1371/journal.pwat.0000272.g003

Eighty percent (n = 80/100), 97% (n = 108/111), and >99% (n = 602/603) of BW, HTTW and TW samples, respectively, exceeded the effects-screening-level of concern, while 54% (n = 54/100), 83% (n = 92/111), and >99% (n = 598/603) of BW, HTTW and TW samples, respectively, exceeded the benchmark equivalent concentration. This indicates a high potential for health risk due to lifetime consumption of water from each of the drinking water options tested, with the highest potential hazard posed by TW and the lowest by BW. These ∑ TQ results agree with those of prior studies of both nationwide POU TW and BW [ 33 – 35 , 41 ], though Bradley et al. [ 24 ] saw a higher proportion of effects-screening-level and benchmark equivalent concentration exceedances for BW. The mean (and standard deviation) of ∑ TQ was 12.0 (±23.5), 20.3 (±39.6), and 130.3 (±75.4) in BW, HTTW, and TW, respectively, indicating the disproportionately higher potential toxicity of TW compared with BW and HTTW (Table H in S1 File ).

Drinking water option was significantly associated with cumulative toxicity quotient outcomes using Welch’s one-way ANOVA (F = 502.44, p<0.0001) to account for unequal variance [ 77 ] (Tables A and B in S1 Text ). Effect size as measured by omega-squared was large (0.77; Table C in S1 Text ). This finding was robust to a sensitivity analysis removing outliers. Overall, Games-Howell posthoc tests indicated the average TW sample had significantly higher potential toxicity than that of both HTTW and BW samples (p<0.0001), whereas the average HTTW and BW sample had no significant difference in mean toxicity quotients ( Fig 3 ; Table D in S1 Text ). While mean differences were insignificant between BW and HTTW, the variability of HTTW ∑ TQs was greater than that of BW ∑ TQs (Table H in S1 File ), as indicated by a wider interquartile range (1.3–18.4) compared with that of BW (0.2–12.2). This suggests that HTTW had slightly more variability in potential toxicity at a sample level. This likely reflects the range of technologies applied to the HTTW samples, which included sediment filters, carbon-based filters, reverse osmosis, ion exchange, distillation, KDF filters, UV disinfection and unspecified filtration.

Individual contaminant TQs across samples indicate that, at the sample level, a diverse range of contaminants may be responsible for the potential toxicity of any individual sample (Figs F-H in S1 File ), underscoring the importance of sample-level toxicity assessments to consider exposure risks at a household-level. However, when contaminants are identified for their percent contribution to the overall potential toxicity of a drinking water option ( Fig 4 ; Table I in S1 File ), toxicity mitigation strategies for broader public health improvements can be prioritized, as discussed in the following section.

https://doi.org/10.1371/journal.pwat.0000272.g004

Consistent with the exceedance results in Section 3.2 and findings in Bradley et al. [ 24 ], THMs–driven primarily by chloroform–were responsible for most of the potential toxicity for all three drinking water categories– 79.4%, 76.7%, and 94.5% for BW, HTTW and TW, respectively ( Fig 4 ; Table I in S1 File ). Addressing chloroform and THMs generally is important across all drinking water options, but Fig 4 (and Table I in S1 File ) illustrates that 94.5% of potential toxicity as determined by the 100 analytes evaluated in TW samples would be addressed at the tap by treating THMs (0.87% of total potential toxicity is contributed by bromodichloromethane which is displayed in the “Other” group in Fig 4 ).

The remaining risk for TW and HTTW was primarily driven by lead, with contributions from other metals (including nickel, copper, cadmium and cobalt), geogenic elements (arsenic and uranium) and fluoride for HTTW, while the remaining risk for BW was driven by geogenic elements (including lithium, uranium, boron and arsenic). In the case of HTTW, potential toxicity was composed of a wider range of compounds–likely because many household treatment technologies are mitigating trihalomethanes and thus other unaddressed contaminants drive overall toxicity.

3.4 Implications for toxicity mitigation

Taken together, the absolute exceedances and cumulative toxicity results have a range of implications for consumer choice among BW, HTTW and TW. First, analytes impacting taste thresholds exceeded benchmarks in TW and HTTW samples more than in BW samples, supporting evidence that aesthetic differences between TW and BW may drive consumers toward BW. However, cumulative toxicity results indicate that BW is not free from exposure risk despite emphatic marketing otherwise. Though not addressed in this study, the environmental and financial burden of BW is also substantial when compared with those of HTTW and TW–environmental impacts of BW are orders of magnitude greater than that of TW [ 78 , 79 ] and the price of BW exceeds that of HTTW or TW by thousands of dollars per year [ 17 ]. While BW may be preferable for a temporary period where TW is declared unsafe, HTTW is likely a more affordable and sustainable option where aesthetic issues and potential toxicity risk persist in TW [ 80 ]. This is supported by the finding that the difference in mean cumulative potential toxicity was insignificant between HTTW and BW.

While HTTW has the potential to mitigate certain contaminants, potential toxicity was still identified in HTTW samples. This underscores the importance of technology selection tailored to POU water quality and ongoing user maintenance to ensure HTTW efficacy. Fig 4 demonstrates the potential mitigating effect of household treatment on disinfection byproducts relative to TW and illustrates the diverse range of contaminants that contribute to the toxicity of these samples overall. The wide range of contaminants found in HTTW samples would likely be reduced if treatment technology were chosen in accordance with POU water quality. Further research to support user compliance and maintenance of treatment devices, perhaps in partnership with utilities, is warranted.

Third, TW and HTTW samples had higher exceedances and potential toxicity than BW from metals commonly used in distribution systems, plumbing, and fixtures. For example, lead was detected in 51% of TW samples and 30% of HTTW samples (but only one BW sample), and contributed 2.9% and 6.6% of overall toxicity to TW and HTTW, respectively ( Fig 4 ). Lead is a well-studied problem that has garnered significant policy response–the recently proposed Lead & Copper Rule Improvements would require utilities to replace all lead service lines within 10 years [ 81 ]. While this should reduce lead levels in TW and HTTW, it has been over 30 years since the original Lead & Copper Rule was established [ 54 ] and almost 10 years since the Flint, MI water crisis. Policy can be slow to address even well-understood contaminants, and other metals–like cobalt, nickel, and cadmium detected in TW and HTTW samples–have diverse sources that may be more challenging to mitigate through targeted policies. In such cases, properly designed, targeted household-scale treatment may be an effective intervention to reduce toxicity further than currently possible with drinking water standards. Some cities have begun to implement this, for example Denver Water delivered free pitcher filters to households to support their lead remediation goals [ 82 ].

Finally, targeted treatment for THMs would reduce the risk profile for all drinking water options, but would have the greatest impact in TW. Given the prevalence of surface water-supplied water systems in the San Francisco Bay Area, THMs will likely persist above health protective benchmarks, but below regulatory standards, if current water treatment practices continue. At least 68% of treatment systems for HTTW samples included carbon-based filters, which should be effective in reducing THM concentrations, and HTTW samples had much lower THM concentrations than TW samples in this study. Given the gap between regulatory standards and health benchmarks for THMs, treatment at home may be the only near-term strategy for mitigation of THMs to health-protective levels. Further THM mitigation in TW is important even if BW is the primary drinking water source for a household, as most people still use TW or HTTW for other domestic purposes and would be exposed to THMs via inhalation [ 79 , 83 ].

3.5 Study limitations

This study addresses several limitations of previous studies, with the inclusion of a large sample size of BW products representative of San Francisco Bay Area consumer choices, an unprecedented number of in-home TW quality results, and “in practice” water quality from people treating their water at home. Still, there are known limitations of this study and areas for future research. First, while data was produced using EPA approved methods, commercial laboratories often have higher detection limits than academic or agency laboratories; several differences in these findings from the recent study on BW by Bradley et al. [ 24 ] indicate differences in analytical sensitivity.

Second, the cumulative toxicity quotient approach assumes that contaminant impacts are cumulative, though some chemicals may be more or less than additive [ 84 ]. The approach is also limited by the analytical scope of the study (conservative with respect to the full range of potential contaminants present) and availability of health benchmarks. For example, various organic contaminants that were not measured here–such as pesticides, PFAS compounds, phthalates and additional DBPs–have been detected in BW in prior studies [ 24 , 28 , 31 , 85 ]. The limitation of scope is also salient in the case of DBPs. There are over 700 known DBPs, many of which are more toxic than THMs, and THMs are not necessarily good surrogates for other DBPs, especially iodine- and nitrogen-containing DBPs that can be formed at higher levels when chloramines are used as disinfectants [ 57 , 86 ]. Thus, it is expected that a broader contaminant panel would indicate further contamination challenges across the three water sources, with unique issues for BW.

The representativeness of the TW and HTTW results is another potential limitation. Samples were taken by individuals in the San Francisco Bay Area but not with explicit representation across water systems, though most water systems had similar water source types and treatment practices. Fig B in S1 File indicates a bias over-representing the five southern counties of the San Francisco Bay Area with respect to the location of samples. The large sample size of results across the nine-county area reflects a range of scenarios, but research into the defining characteristics of people analyzing their tap water would allow for a better characterization of bias in the citizen science data.

Lastly, detailed statistical analyses of source water impacts on toxicity profiles (i.e., surface water versus groundwater versus mixed-sources) were not possible given the available data (see Table F in S1 File ), and future research into this area would support more targeted toxicity mitigation efforts.

4. Conclusions

Alternatives to tap water, including household-scale treatment of tap water and bottled water, are increasing in popularity but information regarding their water quality is limited. This is the first large-scale study comparing the water quality of the realistic consumer drinking water options of bottled water, tap water, and household-treated tap water. Potential aesthetic concerns were identified in all drinking water options, but were more common in TW and HTTW samples, supporting previous evidence that people switch to BW in response to aesthetic concerns. Potential toxicity of samples was also identified despite the quality of the municipally supplied water in the study being largely within state and federal drinking water limits, and the BW quality mostly falling within FDA standards.

Overall, TW had significantly higher average potential toxicity than BW and HTTW. Potential toxicity in all three water sources was primarily attributed to THMs, followed by metals for TW and HTTW, likely derived from distribution systems, household plumbing and/or fixtures, and geogenic elements in groundwater-derived BW and HTTW. Improving THM management across all three water sources would have a significant impact on the cumulative potential toxicity of samples. Average potential toxicity of samples was not significantly different between HTTW and BW, suggesting that BW–which has higher environmental and financial costs than HTTW–is not a superior alternative to TW where household treatment is possible. Persistent aesthetic issues and potential toxicity in HTTW could be addressed by designing household-scale treatment to specifically address identified issues, perhaps in partnership with water systems. This approach is not common and represents an area for future research and policy design to achieve safe water goals. Evidence is provided showing higher water quality among households using household-scale treatment as compared with those using TW, which indicates that treatment at POU can address water quality issues and thus may be a tractable complement to improved TW to improve public health.

Supporting information

https://doi.org/10.1371/journal.pwat.0000272.s001

S1 Text. Methods, ANOVA, and Posthoc tests.

https://doi.org/10.1371/journal.pwat.0000272.s002

Acknowledgments

The bottled water sample collection and analysis was funded by SimpleLab, Inc. We thank Noor Brody for technical review of early versions of the analysis, Alea Laidlaw for research assistance at the project’s inception, and eight anonymous experts for their support on study design. Finally, we thank Carsten Prasse for providing us with critical feedback on the original manuscript.

• 1. Riggs , Hughes J, Irvin D, Leopard K, Riggs E Irvin D, Leopard K HJ. An Overview of Clean Water Access Challenges in the United States. Chapel Hill: US Water Partnership; UNC Environmental Finance Center; 2017. Available: https://www.urbanwaterslearningnetwork.org/wp-content/uploads/2019/05/UNC-Clean-Water-Access-Challenges2017.pdf
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• Published: 17 July 2020

The quality of drinking and domestic water from the surface water sources (lakes, rivers, irrigation canals and ponds) and springs in cholera prone communities of Uganda: an analysis of vital physicochemical parameters

• Godfrey Bwire   ORCID: orcid.org/0000-0002-8376-2857 1 ,
• David A. Sack 2 ,
• Atek Kagirita 3 ,
• Tonny Obala 4 ,
• Amanda K. Debes 2 ,
• Malathi Ram 2 ,
• Henry Komakech 1 ,
• Christine Marie George 2 &
• Christopher Garimoi Orach 1  

BMC Public Health volume  20 , Article number:  1128 ( 2020 ) Cite this article

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Water is the most abundant resource on earth, however water scarcity affects more than 40% of people worldwide. Access to safe drinking water is a basic human right and is a United Nations Sustainable Development Goal (SDG) 6. Globally, waterborne diseases such as cholera are responsible for over two million deaths annually. Cholera is a major cause of ill-health in Africa and Uganda. This study aimed to determine the physicochemical characteristics of the surface and spring water in cholera endemic communities of Uganda in order to promote access to safe drinking water.

A longitudinal study was carried out between February 2015 and January 2016 in cholera prone communities of Uganda. Surface and spring water used for domestic purposes including drinking from 27 sites (lakes, rivers, irrigation canal, springs and ponds) were tested monthly to determine the vital physicochemical parameters, namely pH, temperature, dissolved oxygen, conductivity and turbidity.

Overall, 318 water samples were tested. Twenty-six percent (36/135) of the tested samples had mean test results that were outside the World Health Organization (WHO) recommended drinking water range. All sites (100%, 27/27) had mean water turbidity values greater than the WHO drinking water recommended standards and the temperature of above 17 °C. In addition, 27% (3/11) of the lake sites and 2/5 of the ponds had pH and dissolved oxygen respectively outside the WHO recommended range of 6.5–8.5 for pH and less than 5 mg/L for dissolved oxygen. These physicochemical conditions were ideal for survival of Vibrio. cholerae .

Conclusions

This study showed that surface water and springs in the study area were unsafe for drinking and had favourable physicochemical parameters for propagation of waterborne diseases including cholera. Therefore, for Uganda to attain the SDG 6 targets and to eliminate cholera by 2030, more efforts are needed to promote access to safe drinking water. Also, since this study only established the vital water physicochemical parameters, further studies are recommended to determine the other water physicochemical parameters such as the nitrates and copper. Studies are also needed to establish the causal-effect relationship between V. cholerae and the physicochemical parameters.

Peer Review reports

Water is the most abundant resource on the planet earth [ 1 ], however its scarcity affects more than 40% of the people around the world [ 2 ]. Natural water is an important material for the life of both animals and plants on the earth [ 3 ]. Consequently, access to safe drinking water is essential for health and a basic human right that is integral to the United Nations Resolution 64/292 of 2010 [ 4 ]. The United Nations set 2030 as the timeline for all countries and people to have universal access to safe drinking water; this is a Sustainable Development Goal (SDG) 6 of the 17 SDGs [ 5 ]. The availability of and access to safe water is more important to existence in Africa than it is elsewhere in the world [ 6 ]. Least Developed Countries (LDCs) especially in sub-Saharan Africa have the lowest access to safe drinking water [ 7 ]. In Africa, rural residents have far less access to safe drinking water and sanitation than their urban counterparts [ 8 ].

Natural water exists in three forms namely; ground water, rain water and surface water. Of the three forms, surface water is the most accessible. Worldwide, 144 million people depend on surface water for their survival [ 9 ]. In Uganda, 7% of the population depends on surface water (lakes, rivers, irrigation canal, ponds) for drinking water [ 10 ]. The same surface water is a natural habitat for many living organisms [ 11 ] some of which are responsible for transmission of infectious diseases such as cholera, typhoid, dysentery, guinea worm among others [ 12 ]. Surface water sources include lakes, rivers, streams, canals, and ponds. These surface water sources are often vulnerable to contamination by human, animal activities and weather (storms or heavy rain) [ 13 , 14 ]. Globally, waterborne diseases such as diarrheal are responsible for more than two million deaths annually. The majority of these deaths occur among children under-5 years of age [ 15 ].

Cholera, a waterborne disease causes many deaths each year in Africa, Asia and Latin America [ 16 ]. In 2018 alone, a total of 120,652 cholera cases and 2436 deaths were reported from 17 African countries to World Health Organization [ 17 ]. Cholera is a major cause of morbidity and mortality in Uganda [ 18 ]. The fishing communities located along the major lakes and the rivers in the African Great Lakes basin of Uganda constitutes 5% of the Uganda’s population, however these communities were responsible for the majority (58%) of the reported cholera cases during the period 2011–2015 [ 19 ]. Cholera outbreaks affect predominantly communities using the surface water and the springs. There is also high risk of waterborne disease outbreaks in the communities using these types of water [ 20 , 21 ]. Studies of the surface water from water sources located in the lake basins of the five African Great Lakes in Uganda identified Vibrio. cholerae [ 22 , 23 ] though no study isolated the toxigenic V. cholerae O1 or O139 that cause epidemic cholera. Cholera outbreaks in the African Great Lakes basins in Uganda have been shown to be propagated through water contaminated with sewage [ 20 , 24 ]. Cholera is one of the diseases targeted for elimination globally by the WHO by 2030 [ 25 ]. Hence, to prevent and control cholera outbreaks in these communities, promotion of use of safe water (both quantity and quality), improved sanitation and hygiene are the interventions prioritized by the Uganda Ministry of Health [ 26 ]. Most importantly, provision of adequate safe water is a major pillar of an effective cholera prevention program given that water is the main mode of V. cholerae transmission [ 27 , 28 ].

Availability of adequate safe water is essential for prevention of enteric diseases including cholera [ 29 ]. Therefore, access to safe drinking and domestic water in terms of quantity and quality is key to cholera prevention. Water quality is defined in terms of three key quality parameters namely, physical, chemical and microbiological characteristics [ 30 ]. A less common but important parameter is the radiological characteristics [ 31 ]. In regards to the physicochemical parameters, there are five parameters that are essential and impacts life (both flora and or fauna) within the aquatic systems [ 32 ]. These vital physicochemical parameters include pH, temperature, dissolved oxygen, conductivity and turbidity [ 32 ].

pH is a value that is based on logarithm scale of 0–14 [ 33 ]. Aquatic organisms prefer pH range of 6.5–8.5 [ 34 , 35 , 36 ]. Low pH can cause the release of toxic elements or compounds into the water [ 37 ]. The optimal pH for V. cholerae survival is in basic range (above 7). Vibrio cholerae may not survive for long in acidic pH [ 38 ]. A solution of pH below 4.5 will kill V.cholerae bacteria [ 39 ].

Most aquatic organisms are adapted to live in a narrow temperature range and they die when the temperature is too low or too high [ 34 ]. Vibrio cholerae , bacteria proliferate during algae bloom resulting in cholera outbreaks [ 40 , 41 ]. This proliferation could be due favourable warm temperature [ 42 ]. Relatedly, V. cholerae isolation from natural water in endemic settings is strongly correlated with water temperature above 17 °C [ 43 ].

Dissolved oxygen is the oxygen present in water that is available to aquatic organisms [ 34 ]. Dissolved oxygen is measured in parts per million (ppm) or milligrams per litre (mg/L) [ 35 ]. Organisms in water need oxygen in order to survive [ 44 ]. Decomposition of organic materials and sewage are major causes of low dissolved oxygen in water [ 12 ].

Water conductivity is the ability of water to pass an electrical current and is expressed as millisiemens per metre (1 mS m- 1  = 10 μS cm − 1 ) [ 29 ]. Most aquatic organisms can only tolerate a specific conductivity range [ 45 ]. Water conductivity increases with raising temperature [ 46 ]. There is no set standard for water conductivity [ 45 ]. Freshwater sources have conductivity of 100 – 2000μS cm − 1 . High water conductivity may be due to inorganic dissolved solids [ 46 ].

Turbidity is an optical determination of water clarity [ 47 ]. Turbidity can come from suspended sediment such as silt or clay [ 48 ]. High levels of total suspended solids will increase water temperatures and decrease dissolved oxygen (DO) levels [ 12 ]. In addition, some pathogens like V. cholerae, Giardia lambdia and Cryptosporidia exploit the high water turbidity to hide from the effect of water treatment agents and cause waterborne diseases [ 49 ]. Consequently, high water turbidity can promotes the development of harmful algal blooms [ 41 , 50 ].

Given the importance of the water physicochemical parameters, in order to ensure that they are within the acceptable limits, the WHO recommends that they are monitored regularly [ 51 ]. The recommended physicochemical parameters range for raw water are for pH of 6.5–8.5, turbidity of less than 5Nephlometric Units (NTU) and dissolved oxygen of not less than 5 mg/L [ 51 ]. Surface and spring water with turbidity that exceeds 5NTU should be treated to remove suspended matter before disinfection by either sedimentation (coagulation and flocculation) and or filtration [ 52 ].

Water chlorination using chlorine tablets or other chlorine releasing reagent is one of the most common methods employed to disinfect drinking water [ 53 , 54 ]. Chlorination is an important component of cholera prevention and control program [ 55 ]. In addition to disinfection to kill the pathogens, drinking water should also be safe in terms of physicochemical parameters as recommended by WHO [ 51 ]. However, to effectively make the water safe using chlorine tablets and other reagents, knowledge of the physicochemical properties of the surface and spring water being disinfected is important as several of the parameters affect the active component in the chlorine tablets [ 56 ]. For example, chlorine is not effective for water with pH above 8.5 or turbidity of above 5NTU [ 53 ].

Generally, there is scarcity of information about the quality and safety of drinking water in Africa [ 57 ]. Similarly, few studies exist on the physicochemical characteristics of the drinking water and water in general in Uganda. Furthermore, information from such studies is inadequate for use to increase safe water in cholera prone districts of Uganda where the need is greatest. The cholera endemic communities of Uganda [ 19 , 21 , 24 ] have adequate quantities of water that is often collected from the Great lakes, rivers and other surface water sources located within the lake basins. However, the water is of poor quality in terms of physicochemical and microbiological characteristics. Several studies conducted in Uganda have documented microbiological contamination of drinking water [ 20 , 24 , 58 , 59 ]. However, few studies exist on the physicochemical characteristics of these water. Furthermore, these studies focused on few water sources, for example testing the lakes and omitted the rivers, springs and ponds or testing the rivers and omitted the other water types. One such study was carried out on the water from the three lakes in western Rift valley and Lake Victoria in Uganda [ 23 ], This study did not assess the other common water sources such as the rivers, ponds and springs that were used by the communities for drinking and other household purposes. Other studies on water physicochemical characteristics assessed heavy metal water pollution of River Rwizi (Mbarara district, Western Uganda) [ 60 ] and of the drinking water (bottled, ground and tap water) in Kampala City (Central Uganda) [ 61 ] and Bushenyi district (Western Uganda) [ 62 ]. These studies found high heavy metal water pollution in the drinking water tested. The information gathered from such studies is useful in specific study area and is inadequate to address the lack of safe water in the cholera endemic districts of Uganda where the need for safe drinking water is greatest. Several epidemiological studies in Uganda have attributed cholera outbreaks to use of contaminated surface water [ 20 , 21 , 24 , 63 ]. Furthermore, studies conducted on the surface water focus on pathogen identification [ 63 , 64 ] leaving out the water physicochemical parameters which are equally important in the provision of safe drinking water [ 53 ] and are necessary for survival of all living organisms (both animals and plants) [ 44 ].

Therefore, the aim of this study was to determine the physicochemical characteristics of the surface water sources and springs located in African Great Lakes basins in Uganda so as to guide the interventions for provision of safe water to cholera prone populations [ 19 , 20 , 21 , 24 , 58 ] of Uganda. This study in addition has the potential to guide Uganda to attain the United Nations SDG 6 target of universal access to safe drinking water [ 2 ] and the WHO cholera elimination Roadmap [ 25 ] by 2030. Furthermore, these findings may guide future studies including those on causal-effect relationship between physicochemical parameters and infectious agents (pathogens).

This was a longitudinal study that was conducted between February 2015 and January 2016 in six districts of Uganda that are located in the African Great Lakes basins of the five lakes (Victoria, Albert, Kyoga, Edward and George). These districts had ongoing cholera outbreaks or history of cholera outbreaks in the previous five to 10 years (2005–2015). In addition, the selected study districts had border access to the following major water bodies (lakes: Victoria, Albert, Edward, George and Kyoga). The study area was purposively selected because the communities residing along these major lakes contributed most (58%) of the reported cholera cases and deaths in Uganda [ 19 , 65 ] and in the sub-Saharan Africa region [ 66 ] in the past 10 years. Water samples were collected monthly from 27 sites used by the communities for household purposes that included drinking. Water samples were then tested to determine the vital physicochemical parameters. The water samples were collected from lakes, rivers, springs, ponds and an irrigation canal that were located in the lake basins of the five African Great Lakes in Uganda. In one site, water was also collected from a nearby drainage channel and tested for V. cholerae [ 22 ] and physicochemical parameters. However, because the channel was not used for drinking the results were omitted in this article. Water samples were analysed to determine the pH, temperature, dissolve oxygen, conductivity and turbidity. The study sites were located in the districts of Kampala and Kayunga in central region of Uganda; Kasese and Buliisa districts in western Uganda; Nebbi and Busia districts in northern and eastern Uganda respectively. The study sites were the same as for the simultaneous bacteriological V. cholerae detection study [ 22 ] and are shown in Fig.  1 .

Map showing the location of Uganda, the study districts, major surface water sources and the study sites, February 2015 – January 2016. The blue shades are the African Great Lakes and their basins. (Map generated by ArcGIS version 10.2 [licenced] and assembled using Microsoft Office PowerPoint, Version 2016 [licenced] by the authors)

Rural-urban categorization of the study sites

The study sites were categorized as urban if they were found in Kampala district (the Capital City of Uganda) or rural if they were in the other five remote study districts (Kasese, Kayunga, Busia, Nebbi and Buliisa).

Identification of the study sites and water testing procedures

The sites for water testing were identified with the guidance of the local communities and after direct observation by the study team. Geo-coordinates of the sites were taken at the beginning of the study to ensure that subsequent water collection and measurements were done on water from specific points. Two water collection sites were selected on each of the African Great Lakes in Uganda. The selected sites were in different locations but within the communities with a history of cholera outbreaks in the previous 10 years prior to the study period. For each selected lake point, a site was also selected on a river, a spring and a pond located within the area and being used by the communities for domestic purposes that included drinking and preparation of food. A total of 27 sites, two of which were from each of the five lakes were selected and the water tested. The number of sites on each lake and their locations are shown in Additional file  1 .

Water samples were collected and tested monthly for 12 months by the research assistants who were health workers with background training in microbiology or environmental health. The research assistants received training on water collection and testing from a water engineer. The physicochemical parameters were measured by use of the digital meters namely the Hach meter HQ40d and digital turbidity meter.

Water samples were collected in five-litre containers, three litres were processed for V. cholerae detection by Polymerase Chain Reaction (PCR) test as previously described [ 67 ]. Vibrio cholerae Non O1/Non O139 pathogens were frequently detected in the water samples during the study period [ 22 ]. While the three litres of water were being processed for V. cholerae detection [ 22 ], the rest of the water (2 l), were simultaneously used for the onsite measurement of temperature, pH, conductivity and dissolved oxygen. The Hach meters , HQ40d used in the study, had three electrodes that were calibrated before each monthly testing according to the manufacturers’ manual [ 68 ]. The Hach meter calibrations were done using three specific standard buffer solutions that were for pH, dissolved oxygen and conductivity respectively. Turbidity (total suspended solids or water clarity) was measured using a turbidity meter according to previously published methods [ 49 ]. In addition, the research assistants were provided with Standard Operating Procedures (SOPs) and supervised monthly by the investigators before and during each scheduled monthly measurements.

Data management, analysis and statistical tests

Data were collected, entered, cleaned and stored in the spreadsheet. Errors in the recorded readings were removed using the correct records retrieved from the Hach meters’ HQ40d internal memory. Stata statistical package version 13 was used to analyse the data. Data were analysed to generate means and standard error of the mean for pH, temperature, dissolved oxygen (DO), conductivity (CD) and turbidity. Data were presented in the form of tables and graphs. Comparison for variations between the water samples were carried out using One-Way Analysis of Variance (ANOVA) test. Samples with significant One-Way ANOVA test were subjected to Turkey’s Post Hoc test to establish which of the variables were statistically significant.

The map was created using ArcGIS software, Version 10.2, licenced (ESRI, Redlands, California, USA). The graphs and figures were produced using Microsoft Excel and PowerPoints, Version 2016 (Microsoft, Redmond, Washington, USA). The administrative shapefiles used to create the map were obtained from open access domain, the Humanitarian Data Exchange: https://data.humdata.org/ . In order to generate the study locations on the map, Global Positioning System (GPS) coordinates for the study sites were converted to shapefiles that were combined with the administrative shapefiles corresponding to the locations.

A total of 318 water samples were tested from 27 sites as follows; lake water 40.9%, (130/318), rivers water 26.4% (84/318), ponds water 17.9% (57/318), spring water 11.0% (35/318) and canal water 3.8% (12/318).

Test results for the lake water collected at the fish landing sites (FLS)

The mean physicochemical test results for pH, temperature, dissolved oxygen, conductivity and turbidity are shown in Table  1 .

The mean physicochemical water characteristics of most of the sites were within the WHO recommended water safety range except for turbidity. Few sites had pH and dissolved oxygen outside the WHO recommended safety range.

Monthly variations of the lake water physicochemical characteristics

There were monthly variations in the physicochemical parameters between the water from the lake sites overtime. Most of the sites had steady pH overtime for the first half of the study period (February – August 2015). Thereafter, the pH reduced slightly during the second half (September, 2015 – January, 2016) of the study period. The highest pH fluctuations were in the months of October – December, 2015. The widest change in pH within the same site was observed at Gaaba Fish landing site, Lake Victoria basin, Kampala district.

There were differences in water temperature on the same lake but at different test sites. These differences were detectable mostly in the months of April, 2015. The lowest and highest water temperatures were both recorded on Lake Edward (Kasese district) at Kayanzi fish landing site of 18.9 °C and at Katwe FLS of 34  ° C in the period between April – August, 2015. Fluctuations in the dissolved oxygen were detectable throughout the study period. Kalolo Fish landing site on Lake Albert, Buliisa district showed the widest fluctuations in dissolved oxygen with the highest value of 10.73 mg/L and the lowest of 2.5 mg/L.

Most test sites had small conductivity fluctuations except for Panyimur and Kalolo both of which were located on Lake Albert in Nebbi and Buliisa districts These districts had high water conductivity fluctuations with arrange of 267.1 μS/cm – 2640 μS/cm at Kalolo (Buliisa district) FLS and 296 μS/cm – 2061 μS/cm at Panyimur (Nebbi district). Water turbidity for the majority of the sites changed overtime. Kahendero fish landing site (Lake George, Kasese district) had the highest turbidity which was most noticeable in the months of October 2015 to January 2016. Majanji fish landing site (Lake Victoria, Busia district) had the lowest and most stable water turbidity. Monthly variations of the lake water physicochemical parameters are shown in Fig.  2 .

Monthly variations of lake water physicochemical characteristics (pH, temperature, dissolved oxygen, conductivity and turbidity), February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) water dissolved oxygen; Part d ) water conductivity variations; Part e ) water turbidity variations

River water physicochemical parameter test results

The mean physicochemical characteristics of water from the seven rivers studied are shown in Table  2 .

There were variations in the mean pH, temperature, dissolved oxygen and conductivity between study sites on the rivers. However, these mean parameter variations were in WHO acceptable drinking water safety limit except for River Lubigi, Kampala district which had mean dissolved oxygen below the recommended WHO range. At one time (February, 2015) River Lubigi had dissolved oxygen of 0.45 mg/L. The river water turbidity for all the test sites were above that recommended by WHO of less than 5NTU.

Monthly variations of the river water physicochemical characteristics

Monthly variations in the water physicochemical characteristics of the seven river test sites are shown in Fig.  3 .

Monthly variations of the physicochemical characteristics of river water, February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) water dissolved oxygen variations; Part d ) water conductivity variations; Part e ) water turbidity variations

There were variations in the water physicochemical parameters between rivers and within the same river overtime. Most rivers showed fluctuations of water pH and temperature. Some rivers such as R. Nyamugasani and R. Lhubiriha both in Kasese district had wide temperature fluctuations. River Mobuku (Kasese district) had the lowest water temperature recorded over the study period. Fluctuations in dissolved oxygen were highest in R. Lubigi (Kampala district), Lake Victoria basin. Dissolved oxygen for R. Lubigi was below the recommended level of more than 5 mg/L for most of the study period. Seasonal variations of water dissolved oxygen were also more noticeable in R. Lubigi than the rest of the river sites. Relatively more dissolved oxygen was found during the rainy seasons (March – July, 2015, first rainy season and September – December, 2015, second rainy season) than in dry season.

There were small variations in the water conductivity in the majority of the rivers. Wide fluctuations in conductivity were observed for water samples of R, Lubigi (Kampala district). River Nyamugasani (Kasese district, Lake Edward basin) had steady but higher conductivity than all the other rivers. There were variations in turbidity within the same river overtime and between the different rivers. River Sio (Busia district) had the highest and the widest turbidity variations during the study period.

Water test results for the springs and ponds

The mean physicochemical characteristics of spring and pond water are shown in Table  3 .

The mean physicochemical characteristics of water from the springs and ponds showed variations between the sites. The majority of site means values were within the WHO accepted pH range. Two sites, Wanseko pond (Buliisa, district, Lake Albert basin) and Katanga spring (Kampala district, Lake Victoria basin) had mean water pH below the recommended WHO drinking water acceptable range at the acidic level of 5.73 and 6.19 respectively. Forty percent (40%, 2/5) of the ponds and 33% (1/3) of the springs had mean dissolved oxygen below the recommended WHO level. The ponds with the low dissolved oxygen were found within Lake Albert basin. Among the springs, Katanga spring (Kampala district, L. victoria basin) had mean dissolved oxygen that was below the WHO recommended level of 5 mg/L. Conductivities of the spring water were 89.81–3276.36 μS/cm and for ponds 55.99–3280.83 μS/cm. For both the springs and the ponds the differences between the lowest and the highest conductivities were wide.

Monthly variations of the springs and ponds water physicochemical characteristics

The monthly variations of spring and pond water physicochemical characteristics are shown in Fig.  4 .

Monthly variations of the physicochemical characteristics of the spring and pond water, February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) dissolved oxygen variations; Part d ) conductivity variations and Part e ) water turbidity variations

There were variations in the water physicochemical characteristics of the spring and the pond water overtime. The variations in water (springs and ponds) were also present between the different sites. The springs had small monthly variations of the water physicochemical parameters while the ponds had wide variations. Mughende pond (Kasese district) had the highest pH for most of the study period. Katanga spring (Kampala district) had the lowest pH compared to other springs during the study period. Kibenge spring (Kasese district) had higher temperature than the rest of the two springs (Katanga spring, Kampala district and Nyakirango spring, Kasese district). Most springs and ponds had slight fluctuations in dissolved oxygen except for Mughende pond (Kasese district). Most springs and ponds except for Panyimur pond (Nebbi district) had small monthly fluctuations in water conductivity. Kibenge spring and pond (both located in Kasese district) had higher conductivity compared to the rest of the springs or ponds. Mughende spring and pond were outliers with higher conductivity than the rest of the water sites. There were variations in water turbidity with months for both the springs and the ponds. Apart from Mughende pond (Kasese district), the rest of the springs and ponds showed variations that had two peaks, the first peak (May – August, 2015) and the second peak (November – January, 2016).

Test results of the other surface water sources: Mobuku irrigation canal water

Mobuku irrigation canal water, water diverted from Mobuku River for irrigation purposes by the Mobuku irrigation scheme was tested because the local communities were using this water for domestic purposes including drinking. Apart from water turbidity which was above the WHO recommended standard of 5NTU, the rest of the water physicochemical parameters (pH, temperature, dissolved oxygen and conductivity) were in the WHO acceptable range as follow: pH of 7.93 ± Standard Error (SE) of 0.23, temperature of 26.57 °C ± SE of 1.25 °C, dissolved oxygen of 6.38 mg/L ± SE of 0.18 mg/L, conductivity of 69.06 ± SE of 2.57) and turbidity of 28.68 ± SE of 9.06NTU.

Monthly variations of physicochemical characteristics of Mobuku irrigation canal water

There were monthly variations in water physicochemical characteristics of Mobuku irrigation canal. The water pH and dissolved oxygen showed two peaks each. The first peak was in March – May, 2015 and the second peak, August – November, 2015. The variations of the Mobuku irrigation canal monthly water physicochemical parameters over the study period is shown in Fig.  5 .

Monthly variations of the physicochemical characteristics of Mobuku irrigation canal water, February 2015 – January 2016: Part a ) water pH variations; Part b ) water temperature variations; Part c ) dissolved oxygen variations; Part d ) conductivity variations and Part e ) water turbidity variations

Results of statistical tests for the differences within sites overtime and between sites

One-Way ANOVA test.

There were no statistically significant differences within most of the study sites except for sites on the lakes and the rivers where the pH and temperature differences were statistically significantly within sites overtime. Statistically significant differences in the water physicochemical characteristics were observed between sites (all p -value < 0.05) as indicated in the additional file  2 .

Turkey’s post hoc test

There were statistically significant differences for all water physicochemical parameters for both the lake and river sites. For instance, Lake Edward had both the highest temperature (34 °C, May, 2015) which was registered at Katwe FLS (Kasese district) and the lowest temperature (18.9 °C, April, 2015) which was recorded at Kayanzi FLS (Kasese district). The results of the comparison of the physicochemical parameters of the various lake and river sites are shown in Table  4 .

Similarly, comparison of the springs or pond water showed statistically significant differences for most (80% of the total comparison) of the water parameters (pH, temperature, dissolved oxygen and conductivity) apart from the water turbidity. Turkey’s post Hoc test results for the comparison of springs and pond water physicochemical parameters are shown in Table  5 .

This study showed that water for drinking and domestic purposes from the surface water sources and springs in cholera affected communities/districts of Uganda were not safe for human use in natural form. The water samples from the water sources in the study area did not meet the WHO drinking water quality standards in terms of the important physicochemical parameters. In addition, all the surface water sources and the springs tested had turbidity above the WHO recommended level of 5NTU yet the same water were used for domestic purposes including drinking in the natural form by the households. The study also found variations in the other physicochemical parameters (pH, temperature, dissolved oxygen and conductivity) between study sites on the same lake and between the different water sources.

While the majority of the water sources had mean water physicochemical characteristics (excluding turbidity) in acceptable range, few water sources, mainly the sites on Lake George, including the springs and ponds had pH and dissolved oxygen outside the recommended WHO ranges. These water sources that did not meet the WHO drinking water standards could expose the users to harmful effects of unsafe drinking water including waterborne diseases such as cholera. The present study findings of high water turbidity if due to algae bloom could encourage pathogen persistence and infection spread, including V. cholerae bacteria [ 40 , 41 ] resulting in ill-health and cholera epidemics. In addition, the high water turbidity complicates water disinfection as it gives rise to significant chlorine demand [ 53 ]. The increased chlorine demand can be costly and difficult to ensure constant availability for disinfection of water since Uganda and several other developing countries need and receive supplementary donor support [ 69 ].

In regard to temperature, dissolved oxygen and conductivity, the majority of the surface water sources and springs tested met the recommended WHO drinking water standards. However, a few water sources such as River Lubigi in Kampala district had mean dissolved oxygen below the recommended WHO drinking water standards. Therefore, in order to ensure universal access to safe drinking water, the water sources that had vital physicochemical parameters outside the WHO drinking water range could be targeted for further studies.

There were statistically significant differences in the water physicochemical characteristics between the different sites and sources (lakes, rivers, springs and ponds). Despite these differences, the required approaches to ensure safe water access to the communities may not differ across sites. First and foremost, all sites and water types will need measures that reduce the high water turbidity to WHO acceptable levels. Secondly, in few instances, such as the water sources with pH in acidic range (Katanga spring in Kampala district, Lake Victoria Basin and Wanseko pond in Buliisa district, lake Albert basin) in addition to requiring further studies to identify the causes of the low pH (acidity), such water sources may also require the use of water treatment methods that neutralize the excess acidity [ 54 ]. Furthermore, since acidity is usually associated with increased solubility of toxic heavy metals (lead, arsenic and others) [ 34 ], testing such water for metallic contamination may be required. Heavy metal contamination of water causes ill-health due to chronic exposure which is cumulative and manifest late for correction to be done [ 70 ].

The findings of this study also highlight the differences in water quality between the urban surface water sources and springs (Kampala district) and the rural surface sources and springs (other study districts – Kasese, Kayunga, Busia, Nebbi and Buliisa) The water sources that met the WHO recommended drinking water quality standards [ 53 ] were mostly the rural springs and the rivers. However, these differences between the rural and the urban water sources do not alter the required approaches to ensure access to safe water which is by promoting measures that reduce the high water turbidity in combination with water disinfection to remove the pathogens. The relatively good quality of rural water sources compared to the urban ones could have been due to availability of plenty of vegetation in rural setting that filtered the water along the way downstream and possibly low level of pollution from industrial inputs in rural areas than in urban areas [ 71 , 72 ].

In relation to cholera outbreaks in the study communities, naturally, the physicochemical conditions for survival of V. cholerae O1 occur in an estuarine environment and other brackish waters [ 73 , 74 ]. In such circumstances, the favourable physicochemical conditions for V. cholerae isolation are the high water turbidity [ 49 ] and temperature of above 17 °C [ 43 ]. Interestingly, all the surface water sources and the springs tested had favourable physicochemical characteristics for the survival of V. cholerae in terms of these two parameters (high water turbidity and temperature of above 17 °C). Furthermore, two lakes sites (Kahendero FLS and Hamukungu FLS, Lake George, Kasese district) had also favourable mean pH for the survival of V. cholerae of 9.03 ± 0.17 and 9.13 ± 0.23 respectively. Favourable pH for V. cholerae survival in waters of Lake George was previously documented in the same area [ 23 ]. Hence, the frequent cholera outbreaks [ 19 , 20 , 21 , 24 ] in the study area could be attributed to both the favourable physicochemical water characteristics and use of unsafe water.

There were wide variations in conductivity between water sources and within the same source overtime. High water conductivities were recorded in the months of January to March 2015 (dry season), possibly due to high evaporation which increased the concentration of electrolytes present in water. Likewise, two rivers namely. River Lubigi (Kampala district) and Nyamugasani (Kasese district) had higher mean conductivities of 460.51 ± 57.83 μS/cm and 946.08 ± 3.63 μS/cm respectively than for typically unpolluted river of 350 μS/cm [ 75 ]. Consequently, given that the two rivers flow through areas of heavy metal mining (copper and cobalt mines in Kasese district by Kilembe Mines Limited and Kasese Cobalt Company Limited) and industrial activities (Kampala City), it is possible for the high water conductivity to be due to the heavy metal contamination as previously documented in drinking water in South-western Uganda [ 62 ] and Kampala City [ 61 ]. Thus, specific studies are required on water from the two rivers to determine the true cause of the high conductivity and to guide mitigation measures.

Hence, more efforts are required to promote safe water access in Uganda to attain the WHO cholera elimination target [ 25 ] and SDG 6 by 2030 since 26% (36/135) of mean physicochemical water tests did not meet WHO drinking water quality standards [ 53 ]. These findings together with those of the previous studies which demonstrated the presence of pathogenic V. cholerae in the same water sources [ 22 , 23 , 76 ] should guide stakeholders to improve access to safe water in the Great Lakes basins of Uganda holistically. Thus, measures such as promotion of use of safe water (using water disinfection), health education, sanitation improvement and hygiene promotion that address both the water bacteriological contents and physicochemical parameters should be considered in both the short and medium terms. However, long term plan to increase access to safe water by construction of permanent safe water treatment plants and distribution systems (pipes) should remain a top priority.

In the short and intermediate period, focusing on the measures that reduce water turbidity and disinfection of water (to kill microorganisms) should be prioritized so as to facilitate progress towards attainment of SDGs and cholera elimination in the study area. The basis for such prioritization lies in the fact that high water turbidity raises water temperature and prevents the disinfection effects of chlorine on water. These in return promote survival of the microorganisms and consequently cholera and other waterborne disease outbreaks. Furthermore, though boiling of water is feasible and recommended through technical guidelines [ 26 ] since it addresses both turbidity and kills the micro-organisms, it has issues of poor compliance due to lack of firewood which is the main cooking energy source in these communities [ 70 ]. Therefore, alternative safe water provision targeting reduction of high water turbidity and removal of microorganism by special filters such as decanting and sand filters and flocculation agents which do not need heat energy should be promoted [ 77 , 78 ]. Also, there is a need to explore the use of solar energy (solar water purifiers) [ 79 ] in these communities given their location in the tropics where sunshine is plenty. In the minority of situations, in addition to use of above methods to make water safe, there may be a need to employ different approaches of water purification depending on the water source. For example the water sources with lower or higher than recommended pH [ 53 ] (Wanseko pond, Hamukungu and Kahendero FLS on L. George), use of water treatment reagents that are affected by pH such as chlorine tablets should be reevaluated.

In additional to disinfection and turbidity corrective measures for all the water that were studied, each of the springs in the study area (Katanga in Kampala district and Nyakirango and Kibenge springs in Kasese district) will also need a sanitary survey (a comprehensive inspection of the entire water delivery system from the source to the mouth so as to identify potential problems and changes in the quality of drinking water) [ 80 ]. The findings of the sanitary survey should then guide the medium and long term interventions for water quality improvement in areas served by targeted springs. The following are some of the interventions that could be carried out after a sanitary survey: provision of a screen to prevent the entrance of animals, erecting a warning signs, digging of a diversion ditch located at the uphill end to keep rainwater from flowing over the spring area, establishment of an impervious barrier (a clay or a plastic liner) to prevent potential contaminants from entering into the water or and others measures described in the handbook for spring protection [ 81 ].

Furthermore, as a stopgap measure while access to safe water is scaled up, the communities in the study area should be protected from cholera using Oral Cholera Vaccines [ 82 ]. Protection of these communities is necessary since this study shows that favorable conditions for cholera propagation/transmission are present in the water in the study area. The favorable conditions that were documented in this study included the high water turbidity which makes it difficult to disinfect water [ 53 ] and the water temperature of above 17 °C which speeds up the multiplication of pathogens [ 43 ].

In addition, there were some other important study findings that were not fully understood. For example, some water sources (Kibenge spring and pond (located in Kasese district, western Uganda) had extreme vital physicochemical values for both conductivity and water temperature relative to the rest of above 40 °C and 3000 μS/cm respectively. It is possible that the extreme values were due to geochemical effects documented in water sources around Mount Rwenzori [ 83 ]. However, since there was copper and cobalt mining in Kasese district, high water conductivity could have been due to chemical contamination. Similarly, River Lubigi, Kampala district (central Uganda) had very low dissolved oxygen of less than 1 mg/L during some months (for example in January 2015, dissolved oxygen of 0.45 mg/L) which could have been due to organic pollutants from the communities in Kampala City [ 84 ] that used up the oxygen in the water. Also, Wanseko pond (Lake Albert basin, Buliisa district) had low pH of 4.84 in February 2015. Such water with low pH have the potential to increase the solubility of heavy metals some of which make water harmful when consumed [ 85 ]. Therefore, further studies will be required to better understand such extreme values.

Strength and limitations of this study

This study had several strengths. First, the longitudinal study design that employed repeated measurements of water physicochemical characteristics from the same site and source. This design reduced the likelihood of errors that could arise from one-off measurements seen in cross-sectional study designs resulting in increased validity of the study findings. Second, the inclusion of a variety of the water sources from which drinking and domestic water were collected namely, lakes, rivers, ponds, springs and a canal from different regions of Uganda made the findings representative of the water sources in study districts. Third, use of robust equipment, Hach meters, HQ40d [ 68 ] which automatically compensated for the weather changes (corrected for possible confounders and biases) for the parameters that had effect on each other such as raising water temperature impacting on the water conductivity and dissolved oxygen. Forth, purposive selection of the districts with frequent cholera outbreaks, an important waterborne disease that is targeted for elimination locally within Uganda and globally by WHO [ 25 ]. This meant that the findings had higher potential for used by stakeholders targeting to improve access to safe water and those for cholera prevention.

There were also some study limitations. First, though the study identified the favourable conditions (higher than recommended mean water turbidity and temperature of above 17 °C) for cholera in the study area, we could not report on causal-effect relationship between V. cholerae and the parameters studied. Vibrio cholera e pathogens were detected by use of multiplex Polymerase Chain Reaction (PCR). The results for PCR test were interpreted as positive or negative for V. cholerae O1, O139, non O1, and non O139 [ 22 ]. These data were not appropriate for establishment of causal-effect relationship Therefore, further studies using appropriate methods are recommended to establish such relationships.

Second, during some months of the study, water samples could not be obtained from some sources especially the ponds that had dried up during the dry season. The drying up reduced the number of samples collected from these points. However, since the months without water were few compared to the entire study period, the impact of the missing data could have been minimal.

Third, water samples were only tested for the five key physicochemical water characteristics, Vital Signs [ 32 ] however, there are many other parameters that effect survival and health of living things namely, nitrates, copper, lead, fluoride, phosphates, arsenic and others. Studies are therefore required to provide more information on these other parameters not addressed by the current study.

The study showed that surface and spring water for drinking and other domestic purposes in cholera prone communities in Great Lakes basins of Uganda were unsafe in terms of vital physicochemical water characteristics. These water sources had favourable physicochemical characteristics for transmission/propagation of waterborne diseases, including cholera. All test sites (100%, 27/27) had temperature above 17 °C that is suitable for V. cholerae survival and transmission and higher than the WHO recommended mean water turbidity of 5NTU. In addition, more than a quarter (27%) of lake sites and 40% of the ponds had pH and dissolved oxygen outside the WHO recommended range of 6.5–8.5 and less than 5 mg/L respectively. These findings complement bacteriological findings that were previously reported in the study area which found that use of this water increased their vulnerability to cholera outbreaks [ 22 ]. Therefore, in order for Uganda to attain the WHO cholera elimination and the United Nations SDG 6 target by 2030, stakeholders (the Ministry of Water and Environment, the local governments, Ministry of Health development partners and others) should embrace interventions that holistically improve water quality through addressing both physicochemical and biological characteristics. Furthermore, studies should be conducted to generate more information on the other physicochemical parameters not included in this study such as detection of the heavy metal contamination.

Availability of data and materials

The datasets generated and/or analysed during the current study are available in the Mendeley Data repository, https://doi.org/10.17632/57sw2w23tw.1 . The cholera incidence data used to identify the study area were from Uganda Ministry of Health and the district (Kasese, Busia, Nebbi, Buliisa and Kayunga) weekly epidemiological reports.

Abbreviations

Analysis of Variance

Conductivity

Central Public Health Laboratories

Dissolved Oxygen

Delivery of Oral Vaccines Effectively

Fish landing site

Institutional Review Board

Ministry of Health

Nephrometric units

Polymerase Chain Reaction

Sustainable Development Goal

Standard Operating Procedures

United States of America

World Health Organization

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Acknowledgements

The authors are grateful to the following: the district teams and the communities in Kasese, Kampala, Nebbi, Buliisa, Kayunga and Busia districts for the cooperation and support; the Ministry of Health, Makerere University School of Public Health, Dr. Asuman Lukwago, Dr. Jane Ruth Aceng and Prof. AK. Mbonye for technical guidance. The authors are grateful to Dunkin Nate from John Hopkins University for training of the field teams on water sampling and testing. The authors also thank Ambrose Buyinza Wabwire and to Damari Atusasiire for the support in creating the map and statistical guidance respectively. Special thanks to the laboratory teams in the district hospitals; CPHL (Kampala) and John Hopkins University (Maryland, USA) for carrying out the water tests.

This study was funded by the Bill and Melinda Gates Foundation, USA, through John Hopkins University under the Delivering Oral Vaccine Effectively (DOVE) project. (OPP1053556). The funders had no role in the implementation of the study and in the decision to publish the study findings.

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GB, DAS, AKD and CGO conceived the idea. GB, CGO, AKD, MR, HK, AK, TO and CMG conducted the investigation. MR, HK and TO carried out data curation. MR, HK, GB, DAS, CMG, AKD and AK analysed data. GB, DAK, AKD, CGO, MR, AK, TO and CMG wrote the first draft. All authors read and approved the final manuscript.

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This study was approved by the Makerere University School of Public Health Institution Review Board (IRB 00011353) and the Uganda National Council of Science and Technology. Cholera data used in selection of the water bodies and study communities were aggregated disease surveillance data from the Ministry of Health with no personal identifiers. The laboratory reports on the water sources found contaminated during the study period were shared immediately with the district team to ensure that preventive measures were instituted to protect the communities. In addition, the communities served by such water sources were educated on water treatment/purification (filtration, boiling, chlorination, use of Waterguard ).

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Additional file 1..

The number and the type of water sources in each of the lake basins in cholera prone communities of Uganda that were enrolled in the study, February 2015 – January 2016.

Additional file 2.

One Way ANOVA test results for the differences within the study sites overtime (February 2015 – January 2016) and between sites.

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Bwire, G., Sack, D.A., Kagirita, A. et al. The quality of drinking and domestic water from the surface water sources (lakes, rivers, irrigation canals and ponds) and springs in cholera prone communities of Uganda: an analysis of vital physicochemical parameters. BMC Public Health 20 , 1128 (2020). https://doi.org/10.1186/s12889-020-09186-3

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A framework for monitoring the safety of water services: from measurements to security

• Katrina J. Charles   ORCID: orcid.org/0000-0002-2236-7589 1 ,
• Saskia Nowicki   ORCID: orcid.org/0000-0001-9011-6901 1 &
• Jamie K. Bartram   ORCID: orcid.org/0000-0002-6542-6315 2 , 3  

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The sustainable developments goals (SDGs) introduced monitoring of drinking water quality to the international development agenda. At present, Escherichia coli are the primary measure by which we evaluate the safety of drinking water from an infectious disease perspective. Here, we propose and apply a framework to reflect on the purposes of and approaches to monitoring drinking water safety. To deliver SDG 6.1, universal access to safe drinking water, a new approach to monitoring is needed. At present, we rely heavily on single measures of E. coli contamination to meet a normative definition of safety. Achieving and sustaining universal access to safe drinking water will require monitoring that can inform decision making on whether services are managed to ensure safety and security of access.

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Safely managed drinking water services in the Democratic People’s Republic of Korea: findings from the 2017 Multiple Indicator Cluster Survey

Introduction.

Access to affordable, safe drinking water is critical for securing health gains from development. Significant gains were made in water access during the millennium development goal (MDG) period (1990–2015); however, the approach to drinking water safety relied on a binary improved/unimproved categorisation of water source types, approximating a crude sanitary inspection, which inadequately addresses water safety 1 . Building on the achievements of the MDG period, the sustainable development goals (SDGs) include a target for safe drinking water. The associated indicator for this target is based on water quality analysis for a one-off cross-sectional survey of a nationally representative sample of households and the primary water source that they use.

The term ‘safe’ was used in the MDGs (target 7c—‘halve the proportion of people without sustainable access to safe drinking water and basic sanitation’) and again in the SDGs (target 6.1—‘achieve universal and equitable access to safe and affordable drinking water for all’) to emphasise the importance that drinking water should not propagate disease; however, measurement of ‘safety’ has been an ongoing challenge. The intent and operationalisation of the SDGs—through the wording of targets and indicators—was developed through international participatory processes and built on the successes of the MDGs. The negotiations concerning targets and indicators demanded that these be supported by meaningful baseline data. These restrictions constrained the monitoring approach options, in this case to safety as defined by the Joint Monitoring Programme as Escherichia coli and a few selected ‘priority chemical contaminants’. In the coming decade, as we continue to achieve gains in access to water, we need to ensure our monitoring approaches move beyond quality to monitor the safety, and ongoing security, of drinking water services.

In this Special Collection on Monitoring drinking water quality for the Sustainable Development Goals , we reflect on the purposes of monitoring, considering the tools used and their limitations in guiding achievement of that purpose and of progress towards universal use of safe drinking water. Our reflections are framed around the prevention of transmission of infectious disease through drinking water, in both endemic and outbreak forms, and we focus on E. coli as the most common indicator used in drinking water safety monitoring. In developing a framework for monitoring the safety of drinking water safety, we recognise limitations in approaches to delivering safe drinking water, consider the historical pathways that have led us here, and explore opportunities to reimagine monitoring for safe drinking water.

A framework for monitoring drinking water safety

With reference to SDG target 6.1, the aim of drinking water monitoring is to track and advance progress towards universal access to safe drinking water. This indicates two important components of purpose—one concerns the intention to determine levels of coverage and compare them to the goal of universality; the second is the reference to safety as distinct from quality, which requires that the water be judged as to its fitness for human consumption.

The word ‘monitoring’ is defined by the notion of keeping track of something. Scientific dictionaries normally refine this to include two concepts: the ongoing nature of the activity, and the taking of periodic and programmed observations or measurements. Whether implicit or explicit, the definitions convey an understanding that monitoring ought to be designed with reference to a declared purpose, with the resulting data fit for the intended use. Monitoring for different purposes, to inform different decisions, will require different approaches and measures. For example, compliance monitoring tracks performance against a regulated standard such as a chemical or microbiological parameter, whereas operational monitoring tracks performance against process indicator limits such as for turbidity or residual chlorine 2 , 3 .

In Fig. 1 , we present a framework for monitoring drinking water safety. Monitoring (as it relates to prevention of infectious disease transmission through drinking water) is framed in sequential domains of concern, moving from taking single measurements of indicators or contaminants, to interpreting health hazard, tracking safety of services, and finally monitoring the prospective security of safe services. For the purposes of our discussion here, we use the term ‘safe’ to imply potable water, i.e. that which is fit for human consumption. The framework enables us to interrogate the role of indicators in monitoring drinking water safety. Further, we use it to illustrate the constraints, benefits, and interrelationships of different outlooks—in terms of both conceptualising drinking water safety and interpreting the findings of associated monitoring activities.

A framework for monitoring drinking water safety.

Sample: measuring water quality parameters

Water quality is measured to assess potential contamination. The most common measure used to determine microbial drinking water quality is E. coli . Used as an index of certain pathogens or as an indicator of faecal contamination, the presence of E. coli informs on the likelihood that pathogens are present 4 . E. coli are one of a methodologically defined group of indicators, referred to as total coliforms, that includes members of the genera Escherichia , Klebsiella , Enterobacter , Citrobacter and Serratia . Colony count approaches for coliform bacteria have been formally used to manage water quality in the UK since Report 71 5 was published 4 . E. coli were identified in the 1880s 4 , and were suggested as an indicator of water quality in 1892 6 . As ideas on what was required of an indicator organism advanced in the 1960s and 1970s 7 , 8 , E. coli became the preferred indicator of faecal contamination 9 . E. coli were recognised as ‘the more precise indicator of faecal pollution’ 10 because at the time they were thought to originate exclusively from human and warm-blooded animal faeces, in which they are always present in high quantities. Whereas, other coliform organisms were already known to originate from non-faecal sources as well as from faeces, making them less likely to be reliably associated with the presence of human pathogens 9 . Recognition of this, alongside advancements in methods, resulted in inclusion of E. coli as a preferred indicator of faecal contamination in the second edition of WHO’s Guidelines for Drinking Water Quality (GDWQ) in 1993 11 , and in the EU Drinking Water Directive in 1998 12 . In addition to E. coli , a less specific methodologically defined faecal indicator organism group, thermotolerant coliforms, is also recognised as useful in the GDWQ. Thermotolerant coliforms are a sub-group of coliforms, inclusive of E. coli , that grow at 44.5 °C. Use of this elevated temperature is intended to inhibit the growth of non- Escherichia coliforms, but mostly Citrobacter and Enterobacter are reduced, and even then, not all strains of those genera 13 . While fixed ratios of E. coli to thermotolerant coliforms are sometimes reported, this relationship varies widely 14 —including by climate 15 and water type 16 , and by the enumeration method 14 . Thermotolerant coliforms are sometimes referred to as ‘faecal coliforms’, a misnomer as they do not all originate from faeces 17 . An analytical result of zero (or more correctly <1) thermotolerant coliforms in a water sample would imply zero E. coli , but might be more difficult to achieve, whereas a result positive for thermotolerant coliforms does not confirm the presence of E. coli .

Measurement in our framework is the test that can help to assess if a ‘glass’ of water is contaminated, either by direct measurement of contaminants or using indicators. It is worth noting that the volume used in analyses is typically 100 mL, a volume equated with a ‘glass of water’ 18 . The first GDWQ recommended 100 mL sample sizes while also recognising that it would be ‘statistically more meaningful to examine larger samples, possibly 200, 500, or 1000 ml’ 19 .

Quality: interpreting measurements

Measurement results are often interpreted in terms of the hazard they represent. This is too often used to define the quality of water as ‘safe’ or not. For example, water is considered safe with respect to measured parameters if it does not exceed relevant guidelines or standards. This positivist, normative definition assumes that all potential hazards are known, are measurable, and have been considered. Its limitations are exemplified by widespread occurrence of arsenic in groundwater that had been previously declared ‘safe’ in Bangladesh in the 1990s 20 , 21 .

Drinking water may contain numerous potential health threats for which guidelines have not been established due to insufficient or inconsistent evidence, the low-priority given to threats deemed to be ‘only’ locally significant in few settings, and as yet unrecognised hazards. Guidelines are revisited as new evidence emerges. But guidelines (and therefore our understanding of safe water by normative definitions) are constrained: firstly, by practical considerations, such as the limits of readily available detection methods (for which arsenic is again an example 22 ) and treatment technologies; and secondly, by political considerations such as trade-offs among competing hazards as is the case of disinfectants versus disinfection by-products.

Consequently, judgments of safety are assisted by objective definitions. The GDWQ 23 defines safe drinking-water as that which “does not represent any significant risk to health over a lifetime of consumption, including different sensitivities that may occur between life stages”, where significant risk is defined in terms of the tolerable burden of disease of 10 −6 disability adjusted life years per person per year. The UK also uses an objective definition in their water regulations: the term ‘wholesome’ is applied to water that ‘does not contain any micro-organism… or parasite or any substance …at a concentration or value which would constitute a potential danger to human health’ whether or not a standard has been set 24 .

When E. coli is detected, it is interpreted as a health hazard—in keeping with the notion that it is a ‘faecal indicator bacteria’ (FIB), a long-established notion in sanitary microbiology. Several authors have proposed necessary and desirable characteristics of the ideal faecal indicator 25 , 26 , 27 , and reviewed the degree of fit of candidate organisms against them. Here, we selectively use the criteria that are included in the GDWQ. It is important to revisit these criteria to reflect on the role that E. coli performs as the most common measure to assess progress against SDG 6.1. E. coli align with several of the GDWQ criteria: 23 they are (generally) not pathogens themselves; they are universally present in faeces of humans and animals in large numbers; they are present in higher numbers than faecal pathogens; and they are ‘readily detected by simple, inexpensive culture methods’ (p148). However: while the majority of detected E. coli are not pathogens, a significant subset are pathogenic; and while methods may be simple and inexpensive compared to tests for specific pathogens, they remain sufficiently expensive in most settings that they do not meet the intent of this criterion articulated by Medema et al. 9 : that indicator tests should be inexpensive ‘thereby permitting numerous samples to be taken’.

While field tests have been developed, for regulatory purposes, most E. coli tests are undertaken in a laboratory. This requires that a cold chain be maintained during sample transport and that samples be processed within 6 h, which can be logistically and financially problematic, limiting the validity of results due to changes in the sample composition during storage. For example, in Colombia an estimated 30% of rural water samples would require storage for more than 6 h en route to the laboratory 28 .

Three of the WHO FIB criteria are not met by E. coli

Firstly, some E. coli multiply in natural waters. Such growth has been demonstrated in soils 29 , 30 , sediments 31 , and water columns 32 including in drinking water reservoirs 33 . It has also been shown in the biofilms of distribution systems 34 and in handpumps 35 . Conditions for growth require temperatures over 15 °C, assimilable carbon availability, and absence of disinfectant residuals 36 . While these conditions are uncommon in large utility systems in temperate countries, they are common in many other water systems; for example, shallow groundwaters are over 15 °C in much of the world 37 and contain high loads of organic carbon 38 .

Secondly, E. coli are less robust than many pathogens, so they neither persist in water nor respond to treatment processes in a similar fashion to faecal pathogens. E. coli die-off quicker than many viral or protozoan pathogens in surface water and groundwater 39 , 40 , 41 and during treatment 23 . E. coli are larger and have different surface charge characteristics than viruses and, therefore, are more readily trapped in filters and soil matrices 42 . The different behaviour of pathogens and E. coli illustrates why there is no direct correlation between concentrations of indicators and pathogens 43 . This lack of correlation is a limitation of quantitative microbial risk assessment approaches, since health risk from pathogens is extrapolated from E. coli measurements 44 .

Since the presence of E. coli is interpreted as indicating a health hazard, ‘immediate investigative action’ 23 is recommended when E. coli are detected in drinking water. However, because of the limitations described above, presence of E. coli indicates that, at the time the test was taken, there had either been recent faecal contamination, or a large faecal contamination event less recently, or environmental conditions were appropriate for growth of E. coli . Conversely, the absence of E. coli does not definitively confirm the absence of faecal pathogens. To interpret the results of E. coli tests, it becomes necessary to have more information available. Throughout the water safety literature, it is emphasised that E. coli (or FIB) are most useful as a component of a programme of measurements, not as a single test result 5 , 9 , 45 , 46 . We expand on this in the next section.

A single (or infrequent) test of water for E. coli , and subsequent interpretation of the health hazard, is widely understood as water quality ‘monitoring’, but is not able to advance water safety. E. coli , the most common measure of progress towards universal safe water, has strengths and limitations when we try to use it to infer health hazard. If we use an objective definition of safe drinking water, even within the context of infectious diseases, one test is insufficient to identify and manage threats. For E. coli , when the interpretation of the result is also unclear, a gap emerges between measurement and the stated aim of safety. With reliance on E. coli , and in the absence of other information, results are subject to confirmation bias: If E. coli are not detected in a second test then it is often assumed that the first was wrong and there is no health hazard, rather than considering variability in occurrence and detection. Or if an outbreak occurs, detection of E. coli is assumed to confirm that the water represents a health hazard, however, E. coli may be present for reasons other than recent faecal contamination, and without validation testing it is not possible to ascribe the source of the outbreak.

Safety: tracking safety of services

The preceding domain of our framework, focusing on interpreting measurements, deals simplistically with risk in terms of the likelihood of experiencing a hazard (e.g. of contracting a disease) given a specific exposure. Here we consider safety, which is not simply the inverse of hazard. Effective disease prevention demands consistent hazard-free status. A water supply is not ‘safe’ if it produces one glass of hazard-free water, nor if it delivers pathogen-laden water, briefly, once a year. Empirically, even in highly compliant water supply systems, Setty et al. 47 show that disease (diarrhoea) prevalence increased following changes in water quality due to rainfall. The importance of consistency is further illustrated by the modelling work of Hunter et al. 48 , which suggests an increased risk of over 10% in the probability of annual infection from enteropathogenic E. coli (12.7%), Cryptosporidium (18%) and rotavirus (12%) associated with switching from treated to untreated drinking water for 1 day.

Because sampling and analysis provide a snapshot of quality at the moment of sampling; and because samples of water necessarily represent a negligible fraction of the volume and time of water supplied, assessing on-going safety demands that we move from making and interpreting single measurements to planning sequences of measurements i.e. ‘monitoring’.

There is abundant evidence that E. coli concentrations in water vary rapidly and across orders of magnitude. This is true within natural waters due to non-random distribution 49 , from hazardous events 47 or failures in control measures, which routine sampling regimes do not readily capture as they are limited by logistics. For example, samples are disproportionately taken in mornings and on days earlier in the working week to facilitate transport, analysis and reporting during normal work hours 18 . Here, online measures, such as turbidity or chlorine residual, can improve understanding of temporal variability 47 , 50 and interpretation of other measurements.

Measurements only provide evidence of what the quality was, so management approaches that integrate understanding of system performance into planning are needed to oversee water safety on an ongoing basis. Prospective management of safety requires and builds on the knowledge of historical measurements. It combines evidence that a system has reliably delivered potable water, based on a programmed series of measurements, with knowledge that controls are in place to ensure that perturbations do not compromise quality. At this level of the framework, we have moved from a focus on measurements, which inform on the water system safety yesterday (which is what E. coli tests currently help us understand), to consideration of safety for tomorrow. This prospective safety perspective and its emphasis on ensuring adequate conditions is exemplified by sanitary inspection and water safety plans (WSPs).

Sanitary inspection originated as an adjunct, to water quality measurement. Victorian hygiene literature is replete with examples, and almost a century ago, Prescott and Winslow 51 stated that ‘the first attempt of the expert called in to pronounce upon the character of a potable water should be to make a thorough sanitary inspection’. This illustrates understanding that, even in the absence of contamination at a moment of sampling, a system that is vulnerable to contamination is not safe. As bacteriological methods developed, and their limitations were recognised, these preventative approaches continued to be valued. For example, the first edition of the GDWQ stated that, for non-piped systems, ‘considerable reliance must be placed on sanitary inspection and not exclusively on the results of bacteriological examination’ 19 . Equally, it advised managers of untreated water for piped supplies to include in their assessment of safety both frequent bacteriological results showing the absence of faecal coliforms and information on whether ‘sanitary inspection has shown the catchment area and storage conditions to be satisfactory’ 19 .

In the sense used here, a sanitary inspection is a visual inspection of a piece of water system infrastructure, with the objective of identifying physical factors that could facilitate contamination. It is exhaustive in the sense that all observable faults are considered, but not comprehensive in the sense that not all faults are detectable by visual inspection. Sanitary inspection, reviewed and explored substantively in the paper by Kelly and Bartram 52 , is widely used by those working on rural water systems, where it is frequently applied to community water sources such as boreholes with handpumps.

Sanitary inspection was one of the tools that inspired the development of the concept of WSPs, along with the hazard analysis and critical control points (HACCP) approach, failure mode analysis, quality management, and multi-barrier approaches (the importance of these approaches is highlighted in Kelly and Bartram’s 52 results). Indeed, sanitary inspection is a key component of WSPs, which extend the principles of sanitary inspection to the whole system (‘catchment-to-consumer’).

WSPs and similar systematic risk-based approaches have demonstrated benefits for reducing temporal variation in water quality 47 , as well as reducing the health burden 53 . One of the key attributes of a WSP 54 is that there is evidence that a water supply system can achieve safe water through validation and verification procedures. In validation, evidence is gathered that a water system can effectively meet water quality targets; this may use a variety of tools, including challenging a water system with different conditions and organisms. Verification provides ongoing evidence that a water system is delivering water of the desired quality, for which regular E. coli measurements provides a useful tool. With the system performance characterised through validation and verification, an individual E. coli measurement can be meaningfully interpreted.

Monitoring water safety requires frequent data collection, underpinned by knowledge of system performance and maintenance. Furthermore, to be effective, monitoring data must be available and useful for decision makers, and should support stakeholder cooperation rather than threaten it 55 .

Security: ensuring safe services are sustained

As the SDG target of universal access is progressively achieved, the importance of the future sustainability of safe drinking water supply becomes increasingly apparent, i.e. attention turns towards the risk that those with access might experience a reduction of the level of service, or a loss of service 56 . While for the purpose of this article we focus on safety of drinking water for human consumption, the level of service we aim to secure includes the broader aspects of the human right to water on which the SDG indicators are based 57 . Securing appropriate levels of quantity, reliability, accessibility, and affordability of water that is fit for purpose, are essential to achieving the health-based targets that WSPs are designed to meet 58 .

Terms describing sustainability and sustaining services are interpreted inconsistently. While our preceding reflections concern monitoring for sustained achievement of safety and its implied continuation, here we use the term security in a prospective manner similar to that of ‘sustainable development’ i.e. in a sense that differentiates management of the day to day and familiar (safety) from adequacy for the long term and against the unfamiliar (security). We use three factors to illustrate the potential for attained access to be systematically undermined: demographic change, climate change, and increasing water pollution. Although we focus on these three types of systemic change, we recognise that there are others, such as economic volatility and armed conflict, that are important at this final level of the framework.

Demographic trends warn us of impending risks to availability of sufficient quantities of water because of increasing population, and accelerating demand for water as populations change lifestyles with urbanisation and increasing affluence 59 , 60 . In Kenya, for example, water is scarce (647 m 3 per capita in 2006 61 ) and by 2030, the population is projected to increase by over 80%, with a 50% increase in the proportion of urban dwellers. Increases in water demand will coincide for domestic supply, agriculture and industry (supplying both domestic and international markets 62 ), and good regulation will be necessary to prevent damaging shortages.

Further to demographic pressure, climate change will have substantial consequences for water access. Shortages in Cape Town and São Paulo have highlighted the vulnerability of water supplies to climatic events, and the importance of appropriate management 63 . With climate change, more frequent higher intensity rainfall events will increase the risk of infrastructure damage 64 . Rising temperatures and increasing evapotranspiration rates will reduce available water and increase competing water demand for irrigation 65 . And water quality will deteriorate due to heavier and more erratic rainfall 47 , 66 , increasing release of glacial flows with associated geochemical hazards 67 , and increasing salinity from rising sea levels and expanding irrigation.

In addition to climate change impacts, the problem of water quality deterioration is compounded by pollution. Pollution threatens health directly (through contamination of drinking water that treatment processes do not remove) or indirectly (if chemicals make water unpalatable). Thus, increasing pollution threatens to reduce access to safe drinking water; for example, substantial investments are needed in Dhaka, Bangladesh, to ensure continued access where industrial growth has resulted in the need to pump water from over 30 kms away to avoid local pollution 68 . Environmental water pollution is addressed through SDG 6.3: to ‘improve water quality by reducing pollution…’. Realisation of this goal will require combatting pollution from domestic, agricultural and industrial sources.

To ensure we are working towards sustainable access to safe water, we need tools that can measure and track this progress. Without appropriate indicators, we will continue to focus on access rather than sustainability, potentially misdirecting resources.

New monitoring tools are needed to assess security of safe water supplies

The MDGs, and now SDGs, are based on the notion of provision: increasing the proportion of people with reliable access to affordable, safe drinking water. There remain challenges to achieving the SDG target of universal access, especially for difficult-to-reach populations. There are also practical limits of measuring universality. As we approach the target of universality, however, we need to consider how to shift to a security perspective that encompasses sustainability of high levels of service. Thanks to the achievements of the MDGs and SDGs, 71% of the global population have access to safely managed water services 69 . But because of this success, it is now possible and necessary to adopt a security perspective and to target prospective, inter-generational access to safe water in our changing world.

The participatory, political nature of the processes that define global targets and indicators creates a conservative environment that hinders innovation and diffusion-adoption of improved approaches. We argue that now is the time to start planning for 2030 and beyond, to support a change in focus from access to security of sustainable, safe water supply services and to ensure we can provide the level of evidence needed for adoption of better indicators by the United Nations committees and processes. We recall that the initial Rapid Assessment of Drinking Water Quality (RADWQ) research, done in 2004/2005 15 , created a platform for change that advanced a recognition of drinking water quality in the MDGs, and then monitoring of quality in the SDGs. In 2020, 5 years into the SDGs, where are the new tools we will need for 2030 and beyond?

Through our framework for monitoring drinking water safety we have deconstructed ‘drinking water quality monitoring’, reflecting on its purpose and component parts. Measurement of drinking water quality alone will not deliver the changes needed for safe water. We have become highly reliant on E. coli as a means to assess drinking water quality. It is critical that we remember, however, that the goal of safe water supply is fitness for human consumption, not absence of E. coli . There are a range of measurement tools available that can facilitate regular checks to track direct or indirect changes in water quality or system performance. These tools are important, but cheaper, quicker methods to measure water quality parameters are not enough. The usefulness of measures, such as E. coli , in communicating the problem of water quality has to be tempered by the risk that we lose sight of their purpose and neglect the range of tools needed to achieve safe water and to sustain improvements.

To assess and manage the safety and security of drinking water services, we need monitoring that includes more than direct water quality measures. Through our framework we advocate for this next step. For water safety, there has been consistent emphasis in the GDWQ on the importance of frequent water testing being complemented by knowledge of risks from sanitary inspections and accompanied by systematic management approaches like WSPs. Increased regulation of water services can be anticipated to increase data availability 57 and create an opportunity to focus on management indicators for monitoring the application, oversight and audits of WSPs and sanitary inspections.

These practices, supported by routine monitoring, are essential for safety, and they contribute to ensuring security of drinking water services in the face of threats from demographic and climate change, and pollution. To fully progress from ‘safety’ to ‘security’, however, will require innovations in monitoring that go beyond current practices. There is an opportunity to act smartly, invest strategically, and accelerate progress by incorporating a security perspective. This perspective should enable us to account for prospective long-term drivers that threaten the ongoing sustainability of access to safe water.

Data availability

No datasets were generated or analysed during the current study.

Code availability

No code was generated or used during the current study.

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Acknowledgements

K.C. and S.N. are supported by the REACH programme funded by UK Aid from the UK Department for International Development (DFID) for the benefit of developing countries (Aries Code 201880). However, the views expressed and information contained in it are not necessarily those of or endorsed by DFID, which can accept no responsibility for such views or information or for any reliance placed on them. The authors thank the health-related water community for all the discussions that have informed this work.

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Charles, K.J., Nowicki, S. & Bartram, J.K. A framework for monitoring the safety of water services: from measurements to security. npj Clean Water 3 , 36 (2020). https://doi.org/10.1038/s41545-020-00083-1

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New white paper on private wells offers policy recommendations to protect clean drinking water in North Carolina

November 6, 2024

In North Carolina, one in four households relies on a private well as their primary source of drinking water. The state has the highest number of private wells in the nation, yet a lack of regulation poses serious public health concerns. Further compounding the problem, most private well owners are not getting their wells tested, leaving them vulnerable to the health impacts of consuming contaminated water.     

Many harmful contaminants can’t be seen, smelled or tasted and drinking contaminated water has been associated with cancer, cardiovascular disease, pre-eclampsia, neurological disorders, elevated blood lead levels and higher instances of waterborne illness. Additionally, affluent communities are  four times more likely to have their water treated than low-income communities, further exacerbating health disparities.

Policy Options for Protecting North Carolina Communities Served by Private Wells

A  new white paper  published in the  UNC Dataverse  by researchers at the  UNC Institute for the Environment  (IE), in partnership with the UNC  Superfund Research Program  (SRP) in the Gillings School of Global Public Health and the Well Water Pro Bono Project at the UNC School of Law, offers three policy recommendations to protect community members who rely on private wells for drinking water and addresses policy gaps contributing to health inequalities across the state.   

“More Tarheels get their drinking water from private wells than in any other state, yet these wells are almost entirely unregulated,” said  Kathleen Gray , associate professor and director of UNC IE’s Center for Public Engagement with Science and leader of the UNC SRP Community Engagement Core.  “We believe these recommendations can better protect North Carolina communities served by private wells.”   

The white paper identifies cost as one of the most common barriers to testing.  Well owners can get their wells tested by their local health department or use a private lab, though the price and testing methods vary widely across the state. The average cost of routine testing is $150 per year, ranging from $60 to $440 depending on the area.   

In   their first recommendation ,  the authors call for reducing barriers to private well testing by providing free testing to low-income and pregnant individuals, who are particularly vulnerable to the health impacts of contamination.   

After testing, if contamination is discovered, low-income individuals may also have difficulty treating their drinking water.   

The team’s second recommendation would increase funding to and expand the  Bernard Allen Memorial Emergency Drinking Water Fund, a support fund established by the North Carolina General Assembly to assist low-income well users with addressing contamination  caused by  human activity .    

This recommendation would expand the scope of the fund to also address private well contamination from  naturally occurring sources  that exceed a health-based standard . The fund can provide options to the well users, such as other drinking water sources, a water treatment system, drilling a deeper well or connecting the dwelling to a public utility.   

“When testing reveals contamination in drinking water, many low-income households do not have the resources to treat their water and take other health protective actions,” said  Andrew George , community engagement coordinator with UNC SRP and UNC IE. “The ability to address naturally occurring contaminants and additional funding would allow the state’s fund to better reach more low-income families and distressed well users in North Carolina.”   

A recent addition to  residential property disclosure statements  in North Carolina requires sellers to disclose whether a home on a private well has been tested for quality, quantity and pressure. If it has been tested, the seller must provide the date testing occurred.   

The team’s third recommendation would require private well testing before the transfer of real estate, rental or leased properties. The well testing results would be required to be reported in the disclosure statement prior to purchase. Landlords also would be required to conduct routine testing and provide results to tenants.   

“Younger families are most likely to purchase new homes, and requirements for private well testing prior to signing real estate transfers or leases can provide these families an additional layer of protection for their drinking water,” explained  Maria Savasta-Kennedy , professor and supervisor of the Well Water Pro Bono Project at the UNC School of Law.  

The team also prepared policy profiles for each recommendation to illustrate through case studies how these policy changes may make a difference in the state.   

The full white paper and case studies can be found on the  UNC Dataverse .

About the UNC Institute for the Environment and partners

The UNC Institute for the Environment (IE) develops multidisciplinary collaborations to understand major environmental issues and engage myriad academic disciplines, public and private partners, and an informed and committed community. Through IE’s air and water research centers, its community engagement and sustainability initiatives, and field sites and experiential education programs, the IE provides interdisciplinary forums for faculty, students and community partners to meet pressing environmental challenges.      

Andrew George is a community engagement coordinator in the Center for Public Engagement within the UNC Institute for the Environment. He also supports community engagement efforts in the UNC Superfund Research Program (SRP).    

Kathleen Gray is a research associate professor and director of the Center for Public Engagement with Science in the UNC Institute for the Environment. She also leads community engagement efforts in the UNC Superfund Research Program (SRP).   

Maria Savasta-Kennedy is the George R. Ward Term Professor, clinical professor of law and director of the externship program at the UNC School of Law. She supervises the Well Water Pro Bono Project through the School’s Pro Bono Program.   

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Hydrogen Water: Extra Healthy or a Hoax?—A Systematic Review

Gagandeep dhillon, venkata buddhavarapu, harpreet grewal, pranjal sharma, ram kishun verma, ripudaman munjal, ramprakash devadoss, rahul kashyap.

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Correspondence: [email protected] ; Tel.: +1-484-773-7048

Received 2023 Dec 22; Revised 2024 Jan 9; Accepted 2024 Jan 10; Collection date 2024 Jan.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( https://creativecommons.org/licenses/by/4.0/ ).

Hydrogen-rich water (HRW) has emerged as a novel approach in the field of health and wellness. It is believed to have therapeutic antioxidant properties that can neutralize harmful free radicals in the human body. It has also been shown to be beneficial in mitigating oxidative stress-induced damage through its anti-inflammatory and anti-apoptotic pathways. We aim to conduct a systematic review to evaluate the potential benefits of hydrogen-rich water. The review protocol was uploaded on PROSPERO. After the initial search criteria, the articles were reviewed by two blinded investigators, and a total of 25 articles were included in the systematic review. The potential benefits of hydrogen-rich water on various aspects of health, including exercise capacity, physical endurance, liver function, cardiovascular disease, mental health, COVID-19, oxidative stress, and anti-aging research, are a subject of growing interest and ongoing research. Although preliminary results in clinical trials and studies are encouraging, further research with larger sample sizes and rigorous methodologies is needed to substantiate these findings. Current research needs to fully explain the mechanisms behind the potential benefits of hydrogen-rich water. Continued scientific exploration will provide valuable insights into the potential of hydrogen-rich water as an adjunctive therapeutic approach in the future.

Keywords: hydrogen water, hydrogenated water, hydrogen-rich water, antioxidant, anti-apoptotic, anti-inflammatory

1. Introduction

Hydrogen water, also known as hydrogen-rich water or hydrogenated water, is regular water that has molecular hydrogen gas (H 2 ) added to it [ 1 ]. Water can be hydrogenated by dissolving molecular hydrogen gas into water under elevated pressure, resulting in a supersaturated solution. The hydrogen molecules are extremely small, so they can easily penetrate water and stay dissolved for a while [ 1 ]. Hydrogen-rich water has recently gained significant attention as a potential health-promoting beverage. Studies have been done on animals [ 2 ] and humans [ 3 ] in the last few decades using molecular hydrogen-enhanced water showing antioxidant [ 3 ], anti-inflammatory [ 3 ], and anti-apoptotic [ 3 ] effects. Although there has been some research into the benefits of hydrogen-rich water, there is still a long way to go.

Over the last few years, hydrogen-rich water has become the latest trend to target the global market in the health and wellness industry. Studies have been undertaken to understand its potential benefits. A randomized, double-blind, controlled trial [ 3 ] showed that hydrogen-rich water could reduce inflammatory responses in adults, leading to increased antioxidant capacity in healthy adults. Healthy adults consumed either 1.5 L/day of hydrogen-rich water or plain water. Flow cytometry testing of CD4+, CD8+, CD11+, CD 14+, and CD 20+ yielded interesting results. In the hydrogen-rich water group, the CD14+ cell frequency was decreased [ 3 ]. The benefits of hydrogen use have been evaluated in conditions such as cardiac fibrosis, neuronal disease, hepatic injury, radiation-induced disease, diabetes, and many more conditions [ 4 ]. Through this systematic review, we aim to summarize current research findings related to the use of molecular hydrogen-enhanced water and its anti-inflammatory, antioxidant, and anti-apoptotic impact.

2. Materials and Methods

The initial search terms included were “hydrogenated water”, “hydrogen water”, “hydrogen-rich water”, “molecular hydrogen”, “hydrogenated water”, “antioxidant”, “anti-inflammatory”, “anti-apoptotic”, “fatigue”, “oxidative stress”, and “cytoprotective”. This PubMed search yielded a total of 590 articles. Duplicate articles and animal studies were removed. All articles with titles not related to the topic were eliminated. After reviewing the abstracts by two blinded investigators (RD and RM), 30 articles were retained for a final review ( Figure 1 ). Our inclusion criteria were human studies with hydrogen-rich water and comparison groups or pertinent clinical or pathophysiological information in cohort studies, case-control studies, clinical trials, or observational studies. We excluded opinion articles, editorials, and book chapters for this systematic review. We also excluded results on the therapeutic effects of hydrogen gas inhalation and the injection of hydrogen-rich saline, and only included hydrogen-rich water studies.

Material and methods. Identification of studies via databases. PubMed search with 590 articles. Duplicate articles and animal studies were removed. All articles with titles not related to the topic were also removed. After a close review of the abstracts by two blinded investigators, 25 articles were retained for a final review.

Studies were exported from PubMed to Rayyan software ( https://www.rayyan.ai/ ). Two investigators (PS and GD) screened titles and abstracts independently to select appropriate studies. Afterward, the investigators (GD and HG) assessed the full texts of the articles to determine final eligibility. Conflicts were discussed with a non-reviewing investigator (RK) and were resolved. The study was also registered on PROSPERO (CRD42023445460). The final review was conducted with 30 articles ( Figure 1 ).

One of the first documented human studies on hydrogen-rich water was conducted in 2008. An experimental drink was produced by dissolving hydrogen gas into water under high pressure. It was used for patients with type 2 diabetes or impaired glucose intolerance. Common medical disorders like hypertension, diabetes, and atherosclerosis are associated with oxidative stress. Although the sample size was small, drinking hydrogen-rich water did have some benefits in preventing type 2 diabetes mellitus [ 5 ]. Hydrogen-rich water can be consumed orally and can be produced in multiple ways, which include hydrogen-generating tablets, infusion machines, water generators, and ionizers. The effective delivery of hydrogen through inhalation might be difficult. An advantage of using hydrogen-rich water to deliver molecular hydrogen is that it can be easily administered and is portable [ 6 ]. The beneficial effects can be seen even at low concentrations [ 6 ].

We have divided the summary of our findings into the following subheadings ( Figure 2 ).

Summary of benefits of hydrogen-rich water.

2.1. Health Benefits of Hydrogen-Rich Water with Physical Exercise

Physical activity is good for several reasons, offering numerous mental, emotional, and physical benefits [ 7 ]. Studies have also been done to see the effect of physical activity on mental health [ 7 ]. Some advocates of hydrogen-rich water believe that it has the potential to provide multiple health benefits with physical exercise, like enhanced performance and recovery [ 8 ]. Although the data are still limited and inconclusive, studies have shown encouraging results, as discussed below.

Physical exercise can result in increased reactive oxygen species, which can cause damage to tissue and fatigue. With most forms of exercise, sensations of fatigue and exhaustion occur after some time. Research has shown that drinking hydrogen-rich water before exercising can mitigate the effects of fatigue and build endurance [ 8 ]. A study conducted on cyclists showed that a 7-day consumption of nano-bubble hydrogen-rich water improved the anaerobic performance of trained cyclists compared to that of untrained ones [ 9 ]. There is a build-up of lactic acid in the muscles with exercise. Hydrogen-rich water administered pre-workout showed decreased blood lactic acid levels at a higher intensity and improved ventilatory efficiency [ 10 ]. Pre-workout hydrogen-rich water has also been gaining traction. The supplementation of hydrogen-rich water prior to exercise in other studies has been shown to reduce fatigue as well as improved endurance in the later stages of repeated sprints [ 11 ].

Not all studies have demonstrated encouraging results. A randomized, double-blind, placebo-controlled crossover design study by Botek et al. [ 12 ] showed unclear effects on fatigue. Study participants were placed in either placebo or hydrogen-rich water groups. Interestingly, hydrogen-rich water had an unclear effect on race time and minimal impact on heart rate. Endurance performance was improved by 1.3% in the slowest runners with pre-race hydration with 1680 mL hydrogen-rich water, but the effect on the fastest runners was unclear as there was 0.8% deterioration. Also, in the slowest runners, there was an improvement in race heart rate by 3.8%, along with an improvement in performance; however, in the fastest runners, the change was unclear (0.1%). Depending on the running ability of individuals, the effect of hydrogen-rich water on performance can vary [ 12 ].

Training and competition are part of athletes’ lives. Oxidative stress has a vital role in the development of inflammation [ 3 ]. A study was undertaken on female juvenile soccer players from Suzhou, China, with the consumption of hydrogen-rich water for 2 months in the treatment group, which showed changes in serum malondialdehyde, interleukin-1, interleukin-6, and tumor necrosis factor-α (TNF-α) levels, with an increase in serum superoxide dismutase and total antioxidant capacity levels [ 13 ]. After 8 weeks, serum malondialdehyde levels decreased from 13.80 ± 3.33 to 12.69 ± 1.94 μM in the hydrogen-rich water group and from 16.67 ± 4.19 to 15.79 ± 3.07 μM in the control group ( p = 0.000). In the same period, the interleukin-1 levels went up from 29.32 ± 7.09 μM to 34.47 ± 6.22 μM in the hydrogen-rich water group and from 32.56 ± 7.61 to 42.94 ± 6.24 μM in the control group ( p = 0.002) [ 13 ]. The levels of interleukin-6 increased from 8.74 ± 2.57 to 12.37 ± 3.2 ng/L in the hydrogen-rich water group and from 10.53 ± 1.62 ng/L to 24.88 ± 6.11 ng/L in the hydrogen-rich water group after 8 weeks ( p = 0.000). The serum TNF-α levels increased from 49.46 ± 11.59 to 107.00 ± 13.89 μM in the hydrogen-rich water group and from 60.57 ± 10.09 to 132.24 ± 10.46 μM in the other group ( p = 0.000). For superoxide dismutase, the levels decreased from 14.07 ± 1.91 to 13.69 ± 2.10 U/mL in the hydrogen-rich water group, while it decreased from 13.14 ± 2.18 to 13.01 ± 1.08 U/mL in the control group ( p = 0.027) [ 13 ].

Studies have shown the antioxidant, anti-apoptotic, cytoprotective, and anti-inflammatory properties that hydrogen can exert on the cell. Hydrogen-rich water has the potential to be used for the treatment of many diseases, including cardiovascular and neurodegenerative diseases, among others [ 14 ].

Hydrogen-rich water can improve acidosis due to exercise, energy levels, and enhanced muscular performance in athletes [ 15 ].

2.2. Impact of Hydrogen-Rich Water on Oxidative Stress

Oxidative stress is known to be a common cause of lifestyle-related diseases, the aging process, and even cancer [ 4 ]. Reactive oxygen species are generated internally as we breathe and consume oxygen [ 4 ]. Hydrogen is effective against oxidative stress and is also known for its anti-inflammatory [ 4 ] and anti-allergy [ 4 ] benefits. Hydrogen reduces the oxidative damage that occurs between biological molecules and hydroxyl radicals [ 1 ]. With this reduction in oxidized macromolecules, there is a decrease in cellular and mitochondrial injuries [ 1 ]. Another added advantage is that, even at higher concentrations, hydrogen has no cytotoxicity [ 4 ]. Also, in mixed deep diving gas, hydrogen gas in high concentrations is used for inhalation to prevent arterial gas thrombi and to prevent decompression sickness [ 4 ].

2.3. Impact of Hydrogen-Rich Water on Cardiovascular Health

The effects of molecular hydrogen on cardiovascular disease are interesting. Molecular hydrogen controls signal transduction and gene expression, suppressing pro-inflammatory cytokines and decreasing reactive oxygen species production. It also leads to the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant transcription factor. Even though hydrogen has antioxidant, anti-inflammatory, and anti-apoptotic effects, the exact mechanism of action is poorly understood. There are data to suggest that the mild hormetic-like effects of hydrogen might be responsible for these benefits, but more research is still needed [ 1 ].

Hydrogen-rich water can help in the management of hyperlipidemia [ 16 ]. Twenty patients (10 smokers and 10 non-smokers) who received hydrogen-rich water for 10 weeks showed a drop in total cholesterol levels from 6.42 mM to 5.47 mM ( p < 0.01), whereas LDL levels dropped only from 3.96 mM to 3.24 mM ( p < 0.05). It is interesting to note that the beneficial effects were better in smokers than non-smokers. Additionally, there was no effect on the levels of HDL-C. The levels of serum triglyceride were decreased with hydrogen-rich water treatment in smokers from 2.93 mM to 2.3 mM, but the levels in non-smokers went from 1.49 mM to 1.67 mM [ 16 ].

Hydrogen-rich water can potentially decrease LDL-C and apoB levels while improving HDL function. It may also have a role in the prevention of metabolic syndrome [ 16 ]. In another study [ 17 ], 20 subjects were selected for an 8-week study. Patients with potential metabolic syndrome received hydrogen-rich water (1.5–2 L). There was a 39% increase in antioxidant superoxide dismutase (SOD) ( p < 0.05) and a 43% decrease in thiobarbituric acid (TBARS) in urine ( p < 0.05). Also, high-density lipoprotein (HDL) cholesterol increased by 8%. Fasting glucose levels were unchanged [ 17 ]. A randomized, double-blinded, placebo-controlled trial in 60 individuals with metabolic syndrome yielded encouraging results. Clinical baseline data was obtained at baseline after an observation period of 1 week. Then, subjects were randomized to high-concentration hydrogen-rich water (>5.5 millimoles of H 2 per day) vs. the placebo group. The use of high-concentration hydrogen-rich water was shown to decrease blood glucose and cholesterol levels, improve serum hemoglobin A1c, and also to improve inflammatory biomarkers ( p < 0.05). Interestingly, it also led to an improvement in waist-to-hip ratio and body mass index [ 18 ].

Furthermore, in unstable angina patients, the consumption of hydrogen-rich water with conventional medications was shown to relieve symptoms associated with that condition (60% vs. 90%, χ 2 = 4.800, p < 0.05) [ 19 ]. The hydrogen-rich water group was noted to have lower total cholesterol (35% vs. 15%), apoB (40% vs. 15%), and LDL-C (40% vs. 20%) levels compared to the control group [ 18 ]. Hydrogen-rich water can also improve the endothelial function of the arteries to improve cardiovascular health [ 20 ]. In evaluating vascular endothelial function and cardiovascular disease, the reactive hyperemia index (RHI) using peripheral arterial tonometry (PAT) is useful. RHI improved by 25.4% ( p < 0.05) after 2 weeks of hydrogen-rich water consumption [ 20 ].

2.4. COVID-19 and Hydrogen-Rich Water

The COVID-19 pandemic has significantly impacted our lives in the last few years [ 21 ]. Although it is not a health emergency globally today, it is important to be vigilant as new variants have emerged in the last few years [ 21 ]. It is interesting to note that, as hydrogen inhalation has anti-inflammatory, antioxidant, and anti-apoptotic action, it can aid in the management of COVID-19 [ 22 ]. The antioxidant and biological effects of hydrogen-rich water are seen even after hydrogen is cleared from the body [ 22 ]. Molecular hydrogen therapies were also seen to be effective in remediating the dangerous consequences of COVID-19 infection. Hydrogen administration inhibited cytokine cascade and decreased inhalation resistance in patients with mild to moderate disease [ 23 ]. Although hydrogen has shown potential in the last few years, it is still too early to conclude its usefulness.

2.5. Hydrogen-Rich Water and Dialysis

As we go forward, hydrogen-rich water has started to make an impact on various diseases and disorders. Oxidative stress plays an important role in chronic kidney disease pathology [ 24 ]. In chronic dialysis patients, a study showed that electrolyzed hydrogen-rich water (EHW) intake can improve blood urea nitrogen (BUN) and renal function. It can also decrease oxidative stress in patients with chronic dialysis during their hemodialysis sessions [ 24 ]. Also, in hemodialysis (HD) patients, fatigue is often attributed to oxidative stress. A study was done to see if hemodialysis solutions with electrolyzed hydrogen-rich water would affect autonomic function and fatigue. The use of HD solutions with electrolyzed hydrogen-rich water decreased fatigue in patients on both HD and even on HD-free days [ 25 ]. Alkaline-electrolyzed-reduced water (ERW) has been in use for many years. It has been proven that the primary agent responsible for oxidation reduction potential and the therapeutic effects of ERW was H 2 [ 26 ].

2.6. Effect of Hydrogen-Rich Water on Cancer

As medical science continues to advance, molecular hydrogen has started to find its way into oncology. Colorectal cancer is a common cause of death due to cancer, and removal of tumors is still the mainstay of treatment [ 27 ]. Hydrogen-rich water did show anti-cancer properties in a study [ 27 ]. With its antioxidant properties and ability to decrease oxidative stress, it could be a potential game changer in the future. A combination of hydrogen-rich water and 5-fluorouracil (5-FU) did show improvement in the size of the tumor, fibrosis, and content of collagen [ 27 ]. Another systematic review was to see molecular hydrogen’s effect as an adjunctive therapy for cancer treatment. A total of 677 articles were reviewed, and 27 were selected for final review. Hydrogen was noted to have potential in treatment, overall prognosis, quality of life, and tumor reduction [ 28 ].

2.7. Benefits of Hydrogen-Rich Water on Mental Health

Mental health is another aspect of today’s world that cannot be ignored. As we move on from the COVID-19 pandemic, it is crucial to understand the effect it had on mental health. Higher rates of depression, anxiety, and stress were seen in the general population in many countries [ 29 ]. A study showed that subjects who drank hydrogen-rich water for 4 weeks had improved mood, anxiety, and overall mood [ 30 ]. Another interesting study was performed on women with panic disorder [ 31 ]. The control group was started on psychological treatment and a placebo, while the treatment group was placed on psychological treatment and 1500 mL of hydrogen-rich water daily for 3 months. Results showed no significant difference between the control and treatment groups; however, it should be noted that the treatment group did show a significant decrease in pro-inflammatory cytokines (IL-6, IL-1β, IL-12, and TNF-α) compared to the control group. In the treatment group, after treatment with hydrogen-rich water, IL-1β levels decreased from 94.1 to 65.5, IL-12 from 75.75 to 54.5, IL-6 from 72.3 to 51.67, and TNF-α from 74.5 to 49.25 (all data with p < 0.05). This may have led to an improvement in physical health and body pain [ 31 ].

2.8. Hyroden-Rich Water and Liver Function Benefits

As hydrogen-rich water decreases oxidative stress, a study was done on patients with chronic hepatitis B. Hepatitis B is a global health problem and can be life-threatening. Subjects were administered hydrogen-rich water (1200–1800 mL/day, twice daily), which improved liver function and reduced HBV DNA [ 32 ]. It also decreased oxidative stress in chronic hepatitis B patients [ 32 ]. Non-alcoholic fatty liver disease (NAFLD) affects 25% of the population. Liver dysfunction can be caused by inflammation, oxidative stress, and aberrant cellular signaling. It has been shown that the administration of hydrogen-rich water can have beneficial effects for these patients [ 33 ]. Thirty individuals with NAFLD were administered hydrogen-rich water in a randomized, double-blind, placebo-controlled study for 8 weeks. Decreased body mass index and weight (≈1 kg) were observed in the treatment group [ 33 ]. As treatment for NAFLD remains elusive, a few studies have been done to assess the benefits of hydrogen-rich water on the disease. Hydrogen-rich water was shown to decrease fat accumulation in the liver and has the potential to be used as an adjuvant treatment for mild to moderate NAFLD [ 34 ].

2.9. Effect of Hydrogen-Rich Water on Aging

The risk factor for many cardiovascular diseases, neurodegenerative disorders, and even cancer is age [ 35 ]. With hydrogen-rich water making news in the last few years, a study was undertaken to assess the effects of hydrogen-rich water in men and women above the age of 70 and whether it affected aging. It was found that drinking hydrogen-rich water for 6 months was harmless and also had a favorable effect on many of the factors associated with aging, like pain, metabolic processes in the brain, strength in the lower extremities, etc. [ 35 ]. Another study showed the hydrogen has anti-aging effects through the (Nrf2) pathway on vascular endothelial cells. Therefore, it has the potential to increase longevity. This can even be seen after temporary exposure to hydrogen [ 36 ].

3. Results and Discussion

Hydrogen-rich water has gained worldwide attention over the last few years given its potential health benefits. Hydrogen-rich water’s effect on exercise capacity and physical endurance is of particular interest to individuals with a fondness for physical activity. Additionally, the potential for a positive impact on cardiovascular function can reduce the risk of heart disease. Additionally, the possible effect of hydrogen-rich water on mental health is intriguing, with the initial results being encouraging. Also, its effect on anti-cancer properties holds promise in the field of oncology. Given its potential to positively impact liver function, anti-aging, and oxidative stress, hydrogen-rich water is a subject of ongoing research and growing interest. Hydrogen-rich water offers several potential strengths, including its antioxidant, anti-inflammatory, and anti-apoptotic properties. It can also help decrease oxidative stress. Some studies showed that it may also improve physical endurance, cognitive function, and overall well-being. Moreover, hydrogen-rich water is mostly considered safe, with no to minimal side effects. There is growing interest in the benefits of hydrogen-rich water, and it may also have potential applications in medical therapies.

Hydrogen-rich water can aid in the excretion of toxins from the liver to the bile and promote their fecal excretion by enhancing the efflux pumps of Mrp2 and p -glycoprotein. In a study [ 37 ], there was no effect on plasma mineral ions with a small change in the concentrations of calcium, magnesium, and sulfate between the hydrogen-rich water and control water groups. Interestingly, the hydrogen-rich water group had a higher volume of water intake as compared to the control group, with regular water consumption (81.8 ± 5.1 mL/day in the hydrogen-rich water group compared with 73.9 ± 5.0 mL/day in the control group, p < 0.05). This might have been due to better palatability with the hydrogen-rich water group. Magnesium intake has been shown to decrease cardiovascular and cerebrovascular disease mortality in human beings [ 37 ]. In study [ 37 ], hydrogen-rich water had a higher concentration of magnesium than the control group (22.8 ppm in the hydrogen-rich water group compared to 10.2 in the control group). Magnesium was also shown to decrease levels of blood glucose in rat liver by interfering with the gluconeogenesis pathway. This may have led to a decrease in plasma glucose levels of 7.7% ( p < 0.05) in the hydrogen-rich water group compared to the control group [ 37 ].

Comparison of hydrogen-rich water with other health supplements, such as protein powder, herbal supplements, collagen, and vitamins, is challenging yet essential, as they serve different purposes and can affect health and well-being.

Over the last few decades, protein powder has become popular among individuals with an interest in physical activity looking to support their fitness goals. There have been studies undertaken to assess the impact of protein powders on physical endurance and fitness. In healthy individuals undergoing chronic endurance training, protein supplements were shown to increase aerobic capacity further, improve time trial performance, and lead to lean mass gain [ 38 ]. Another study showed that protein supplements and carbohydrate strategies in individuals undergoing endurance exercise can decrease muscle damage but did not improve endurance capacity [ 39 ]. High protein intake for prolonged periods has been linked to various health concerns, including increased risk of renal disorders, calcium metabolism, the progression of coronary artery disease, and even cancer [ 40 ]. There are not much data available specifically comparing protein powder and hydrogen-rich water strategies for individuals engaging in physical activity.

A separate study was done on 89 individuals to see the effect of protein powder (on whey or casein protein for 12 weeks of consumption) on cholesterol levels [ 41 ]. It caused decreased total cholesterol levels by 7% in the whey protein group compared to the baseline and a 9% decrease in the whey protein group compared to the casein group. LDL levels were also decreased by 7% in the whey group compared to the baseline. Protein powder and hydrogen-rich water can both be a part of a dietary regimen to support fitness goals. While hydrogen-rich water provides potential antioxidant and anti-inflammatory effects [ 15 ], protein supplementation is used for lean muscle gain and increased aerobic capacity. As medical science continues to evolve, we might better understand how these two strategies can be used synergistically or in certain scenarios.

Herbal supplements are commonly used in different parts of the world. A few studies were done to evaluate the impact of herbal supplements on COVID-19 patients. Zinc sulfate could decrease the duration of olfactory dysfunction. However, more well-designed studies are needed in the future given the low quality of included trials [ 42 ]. Also, there has been a debate on using herbal supplements to treat mood disorders. A few are effective in the management of depression, like Catha edulis, Tinospora cordifolia, Curcuma longa, Rhodio larosea, Crocus sativus, etc. [ 43 ]. There has also been evidence in favour of the use of Passiflora spp. (passionflower) and Piper methysticum (Kava) in treating anxiety, and Crocus sativus (saffron ) and Hypericum perforatum (St John’s wort) for treating depression. In schizophrenia, Ginkgo biloba (ginkgo) has been used as an adjunctive treatment [ 44 ]. EGb 761, a special extract of Gingko biloba , stabilizes mood and improves cognitive functioning in elderly individuals with cognitive impairment [ 45 ]. In this study, 176 patients with generalized anxiety disorder or adjustment disorders with anxious mood were randomized to one of the three groups for 4 weeks: 480 mg EGb 761, 240 mg EGb 761, or placebo. The primary outcome measure used was the Hamilton rating scale for anxiety (HAMA). In the high-dose EGb 761 group, the HAMA score decreased by −14.3, −12.1 in the low-dose EGb 761 group, and by −7.8 in the placebo group ( p = 0.0003 in the high-dose group and p = 0.01 in the low-dose group) [ 45 ].

Going forward, there needs to be more focus on quality research to establish herbal supplements’ efficacy and safety as they are not as well established as the psychotropic medications currently in use.

Collagen is associated with skin health and overall well-being. It constitutes approximately 80% of the dry weight of skin [ 46 ]. With aging, there is a decrease in the enzymes involved in its processing that, in turn, decreases the fibroblasts involved in the synthesis of collagen [ 46 ]. Topical and oral collagen can reduce skin aging [ 47 ]. The effects of vitamins and nutrients on aging are also shown [ 46 ]. Supplementation with zinc, carotenoids, selenium, and vitamins C and E could slow aging [ 48 ].

Hydrogen-rich water, protein powder, herbal supplements, and vitamins, etc., are distinct dietary supplements and have different effects on the body. There are not much data available comparing hydrogen-rich water to protein powder, herbal supplements, collagen, and vitamins.

Many factors affect the therapeutic effect of hydrogen-rich water, such as the hydrogen concentration in water, hydrogenation methods, and best duration, etc. This, in turn, can lead to different results. As the hydrogen concentration and quality can vary in studies, it can be challenging to compare results. Although the results of many studies reviewed have been encouraging, it should be noted that many were conducted in animals [ 2 ], and some used small sample sizes [ 48 ]. This can have an impact on the statistical power of the research and the generalizability of findings. Research trials with a large sample size would be needed in the future. We also noticed that the studies on hydrogen-rich water primarily focused on short-term benefits [ 48 ] and did not consider the long-term effects. Some studies [ 16 ] did not have a placebo control group, so it is difficult to determine whether the results could be attributed to hydrogen-rich water.

Also, it should be noted that, as some of the studies might have been supported by organizations with an interest in hydrogen-rich water products, there could be commercial biases in publication. A proper conflict of interest analysis is required as we move forward. Over the last few years, there has been a better understanding of the effects of hydrogen, with studies showing that the primary molecular target of hydrogen is Fe-porphyrin [ 49 ]. The main target of hydrogen intracellularly is mitochondria, where oxidized Fe-porphyrin has been shown to be responsible for hydrogen’s destruction of reactive oxygen species. Fe-porphyrin has also been shown to rectify electron flow in disordered states. Quantum biology going forward can help us better understand the exact mechanism of molecular hydrogen on mitochondria [ 50 ]. Hydrogen-rich water also leads to the activation of Nrf2, which has been shown to have a positive impact on cardiovascular health [ 1 ] and anti-aging effects [ 35 ]. We should look forward to developing therapeutic protocols and validating the potential of hydrogen-rich water in a clinical setting.

4. Conclusions

Increased interest and continuous study are being directed toward the possible health advantages of hydrogen-rich water in a variety of areas, including physical endurance, exercise capacity, cardiovascular disease, liver function, COVID-19, mental health, anti-aging research, and oxidative stress. These potential consequences have aroused debate in the scientific and medical industries. Even though there is great potential in understanding the benefits of hydrogen-rich water, we still have to overcome the existing limitations. We need well-designed studies in humans, with large sample sizes and long-term trials, to ascertain the benefits.

Author Contributions

G.D.—Corresponding author, conceptualization, literature search, original draft. V.B.—Visualization, writing, review and editing, formal analysis. H.G.—Study design, formal analysis, investigation. P.S.—Formal analysis, resources. R.K.V.—Literature search, validation, visualization, resources, methodology. R.M.—Resources, methodology. R.D.—Writing, review. R.K.—Writing, review and editing, supervision. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Data availability statement.

No new data were created.

Conflicts of Interest

The authors declare no conflicts of interest.

Funding Statement

This research received no external funding.

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