Discussion of the optimal mineral composition of drinking water

In our time, there is a boom in clean water. Many city dwellers, who receive seemingly high-quality water from the city water supply, tend to install additional water treatment systems at their homes — most often, reverse osmosis. At the same time, such reasoning is typical: “hard water promotes the formation of kidney stones, causes arthrosis, salt deposition and scum in the kettle, therefore, only desalinated water should be used in everyday life, ideally distillate”. However, in the scientific community there is still no clear answer to the question of whether the use of hard water is associated with the occurrence of urolithiasis. On the contrary, the effect of demineralized water on the human body has been studied quite well, and an unambiguous, consolidated opinion has been formed in the scientific community on this subject.

The myth of the dangers of hard water and the benefits of reverse osmosis

In ancient times, 4.1-3.8 billion years ago, abiogenesis began on the third planet from the Sun. Life slowly began in the primary broth, squinting in the bright sunlight with its small green eyes. Evolutionary development, life adapted to the environment, adapts to it. Years passed, and the first Homo sapiens appeared 300 thousand years ago . They continued the best evolutionary traditions of previous eras, and it should be noted that in all the enclosing landscape, neither then nor now there was no demineralized water anywhere. Well, except for the snow in the Arctic. But there man did not live. And only some 50 years ago the first technologies of deep purification of drinking water appeared. Such a term, by the standards of evolutionary development, is only an artifact within the framework of statistical error. Maybe they were not there, these fifty years. And with the primary broth - a rich mineral solution - life is familiar all my life.

In general, our body is evolutionarily adapted to ordinary natural water, in which some substances are always dissolved. The question is what should be the optimal salinity of drinking water both in quantity and composition. And it should be noted that the first studies on this topic were conducted in the Soviet Union. The material presented below is a free translation of the article “Health risks from drinking demineralized water” ^[1] with my comments and additional sources of information.

Under demineralized water in this text is meant water with an electrical conductivity of less than 20 µS / cm (less than 15 mg / l; for comparison, in ordinary urban water supply, depending on the settlement, water salinity varies from 70 to 250 mg / l) or completely devoid of dissolved minerals as a result of distillation, deionization, membrane filtration or using other technologies for deep water purification. Although deep water purification technologies appeared in the 1960s, demineralized water did not immediately begin to be used for drinking. More often, it has been used in research laboratories as a replacement for distillate. However, in the Central Asian cities of the Soviet Union, even then the water supply problem was acute, which could be solved by desalination plants, therefore, Soviet doctors and scientists were among the first to start investigating the effect of demineralized water on human health. In addition to purely technical problems (demineralized water is extremely aggressive and causes corrosion of water pipes, leaching metals from them), Soviet scientists in the 1960s also pointed to potential health risks lurking in demineralized water. In particular, epidemiological studies have revealed a lower level of cardiovascular diseases and mortality from cardiovascular diseases in areas with hard water compared to areas with soft water. On the other hand, the experience of artificial fluoridation of drinking water has demonstrated a decrease in the incidence of caries among consumers of such water. It became obvious that rationing the salt content of drinking water was necessary not only from above, but also from below, and the search began for the optimum concentration and composition of salts dissolved in water, which led to recommendations later in the 1970s, later adopted by WHO.
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A group of researchers from the Institute of General and Communal Hygiene. A. N. Sysina under the direction of G. I. Sidorenko and Yu. A. Rakhmanin established that “demineralized water has an adverse effect on the organism of animals and humans”. Scientists concluded that the total mineralization of drinking water should be at least 100 mg / l (optimally 200-400 mg / l for chloride-sulphate and 250-500 mg / l for hydrocarbonate waters) with a bicarbonate anion content of at least 30 mg / l, calcium not less than 30 mg / l, alkalinity not more than 6.5 mg-eq / l, sodium not more than 200 mg / l, boron not more than 0.5 mg / l, bromine not more than 0.01 mg / l.

Since then, several decades have passed, and desalination plants have actively entered life, especially in Asia and the Middle East. On an industrial scale, desalinated water, as a rule, is subjected to artificial mineralization with calcium carbonate or by adding a small amount of the original salt water. But this is done mainly to protect water pipes from leaching, and secondly for taste. As a result, people who consume such water (including bottled water) may lose some important chemical elements present in more mineralized water.

Our knowledge of the effects of demineralized water on the body is based on experimental and statistical data. The experiments were carried out on laboratory animals and volunteers, and statistics were collected in regions with a predominant supply of desalinated water in relation to regions supplied with ordinary river or well water. We also have access to the results of epidemiological studies, in which a comparative analysis of the health of the population in areas with a preferential supply of demineralized water compared to areas where ordinary natural water is used was carried out. Possible adverse effects of water consumption with low salinity can be divided into six categories.

1. Direct effects of water with low mineral content on the intestinal mucosa, metabolism, water-salt metabolism and other body functions.

Water with a low content of mineral substances (less than 50 mg / l) has negative taste properties. However, with time you can get used to her taste. However, there is evidence that this water quenches thirst worse. Although it does not directly affect health, this fact should be taken into account. Poor organoleptic and thirst quenching properties can affect the amount of water consumed.

In 1963, Williams claimed in his work that distilled water introduced into the intestine causes abnormal changes in the epithelial cells of rats, possibly due to osmotic shock. However, these findings have not been confirmed by Schumann et al. in later 14-day rat experiments. Histological analysis revealed no signs of erosion, ulceration or inflammation in the esophagus, stomach, and jejunum. In a report prepared for WHO by the group of Yu. A. Rakhmanin in 1980, there was only an increase in the secretion and acidity of gastric juice and a change in the tone of the gastric muscle in rats that were given distilled water. But currently available data clearly indicate a direct negative effect of demineralized water on the gastrointestinal mucosa.

It has been demonstrated that the consumption of water with low mineralization violates the water-salt metabolism. One-year experiments on rats showed that consumption of distilled water or water with a total mineralization of less than 75 mg / l leads to an increase in water consumption, increased diuresis (simultaneous increase in urine and urinary frequency), an increase in extracellular fluid volume and increased excretion of sodium and chloride anions, which leads to a general negative water-salt balance. In addition, there was a decrease in the average red blood cell volume (and other changes in hematocrit ) and a decrease in the secretion of triiodothyronine and aldosterone ; increased secretion of cortisol ; morphological changes in the kidneys, including marked atrophy of the glomeruli and swelling of the vascular endothelium , resulting in restricted blood flow. In embryos of rats whose mothers were given exclusively distilled water, a decrease in skeletal ossification (ossification) was found. At the same time, with the exception of water, the rest of the rats' diet was physiologically adequate in terms of caloric, nutrient and mineral substances. Apparently, a decrease in the consumption of mineral substances from water was not compensated by their content in food.

The results of experiments on human volunteers are consistent with the results of animal experiments. Low mineralized water (less than 100 mg / l) consumed by volunteers resulted in:

but. increased diuresis (on average by almost 20%) and an increase in extracellular fluid volume in the body;
b. increased serum sodium concentration;
at. decrease in serum potassium concentration;
Increased excretion of sodium, potassium, chloride anion, calcium and magnesium from the body.

Low-mineralized water is believed to act on the osmoreceptors of the gastrointestinal tract, causing an increase in the flow of sodium ions into the intestinal lumen and a slight decrease in osmotic pressure in the portal venous system , followed by an enhanced release of sodium into the bloodstream as an adaptation response. This osmotic change in blood plasma leads to a redistribution of water in the body: the total volume of extracellular fluid increases and the transfer of water from red blood cells to plasma. In response to the changed plasma volume, the baroreceptors and the volume receptors in the bloodstream are activated, which leads to a decrease in the release of aldosterone and, consequently, an increase in the elimination of sodium. The reactivity of the volume receptors in the vessels can lead to a decrease in the release of vasopressin ( antidiuretic hormone ) and increased diuresis.

Water in the human body always contains electrolytes (for example, potassium and sodium) in certain concentrations controlled by the body. Resorption (absorption) of water by the intestinal epithelium is provided by active transport (sodium-potassium pump). If distilled water is consumed, the intestine must first add electrolytes to this water, taking them from the body's reserves. Since the body never removes liquid in the form of "pure" water (and only always with salts), it is necessary to ensure an adequate intake of electrolytes. The use of distilled water leads to the dilution of electrolytes contained in body fluids. Inadequate redistribution of water in the body can disrupt the function of vital organs. Symptoms of this condition at the initial stage are fatigue, weakness and headache; in more serious cases, muscle cramps and heart rhythm disturbances appear.

Additional evidence has been obtained from animal experiments and clinical observations in several countries. In laboratory animals, which were given water with the addition of zinc and magnesium salts, a higher concentration of these elements in serum was found than in animals, which were given the same compounds in high doses with food, but were watered with low-mineralized water. Robbins and Sly came to the conclusion that demineralized water leads to significant leaching of micro and macro elements from the body.

Regular consumption of low-mineralized water over many years may not show the symptoms described above. But the enemy does not sleep! Such sweet conditions like hyponatremic shock can occur after intense physical exertion in people who constantly drink demineralized water. The so-called "water intoxication" (hyponatremia shock) can also occur with a single excessive use of not only demineralized, but tap water. A lethal dose of water (LD ₅₀ ) was shown to be 90 ml / kg (rats, oral) ^[2] . A person weighing 70 kg needs to drink only 6.3 l of water in a short period of time in order to cause serious malfunctions in the functioning of the body. At the same time, the “intoxication” risk increases with a decrease in the total salt content. In the past, acute health problems have been noted by climbers who cooked tea and food on melted snow. Heavier version of this condition in combination with brain edema, convulsions and metabolic acidosis was observed in infants whose food and beverages were prepared using low-mineralized or demineralized bottled water.

2. The risk of calcium and magnesium deficiency in the use of softened or low-mineralized water.

Calcium and magnesium play an important role in the body. Calcium is part of the bones and teeth, regulates neuromuscular excitability (reduces it), is responsible for the functioning of the cardiac conduction system, the contractility of the heart and muscles, the transmission of intracellular information and blood clotting. Magnesium acts as a cofactor and activator of more than 300 enzymatic reactions, including glycolysis, ATP metabolism, transfer of sodium, potassium and calcium through membranes, synthesis of proteins and nucleic acids; regulates neuromuscular excitability and muscle contraction.

Despite the fact that water is not the main source of calcium and magnesium, the absence of these elements in drinking water leads to their increased leaching from the body and is not compensated by food intake.

50 years of comparative epidemiological studies around the world have shown that the consumption of water with a low content of calcium and magnesium is associated with increased morbidity and mortality from cardiovascular diseases. Recent studies have also found a connection with the use of soft water in food with a higher risk of fractures in children, some neurodegenerative diseases, preterm birth and pregnancy disorders ( preeclampsia ).

The most valuable information about the effect of low calcium concentrations in drinking water on an entire population of people was obtained in studies conducted in the Soviet city of Shevchenko (now Aktau, Kazakhstan), where desalination plants were used in the city water supply system (the water source is the Caspian Sea). The local population showed a decrease in alkaline phosphatase activity, a decrease in plasma calcium and phosphorus concentrations and an increase in bone decalcification. These changes were most noticeable in women, especially pregnant women, and depended on the length of their stay in Shevchenko. The need for calcium in drinking water is also confirmed in the one-year experiment on rats, which were provided with a completely adequate diet in terms of nutrients and salts, but they were fed with distilled water, to which 400 mg / l calcium-free salts and one of these calcium concentrations were added: 5 mg / l, 25 mg / l or 50 mg / l. In rats treated with water with 5 mg / l of calcium, a decrease in the functionality of thyroid hormones and other related functions was found in comparison with the other animals that participated in the experiment.

It is believed that the general change in the composition of drinking water affects human health over many years, and a decrease in the concentration of calcium and magnesium in drinking water affects our well-being almost instantly. Thus, in 2000–2002, residents of the Czech Republic and Slovakia began to actively use reverse osmosis systems in their apartments for the purification of city water. For several weeks or months, the flow of patients with complaints indicating acute magnesium (and possibly calcium) deficiency swept over local doctors: cardiovascular disorders, fatigue, weakness, and muscle cramps.

3. The risk of a shortage of vital substances and trace elements in the use of low-mineralized water.

Although drinking water, with rare exceptions, is not the main source of vital elements for humans, it can make a significant contribution to their entry into the body for several reasons. Firstly, the food of many modern people is a rather poor source of minerals and trace elements. In the case of a border deficiency of an element, even its relatively low content in the drinking water consumed may play an appropriate protective role. This is due to the fact that elements are usually present in water in the form of free ions and therefore are more easily absorbed from water than food products, where they are mostly found in complex molecules.

Animal studies also illustrate the significance of the micro-sufficiency of certain elements present in water. Thus, according to the data of V. A. Kondratyuk, a slight change in the concentration of trace elements in drinking water drastically affects their content in muscle tissue. These results were obtained in a 6-month experiment in which rats were randomized into 4 groups. The first group was given tap water, the second - low-mineralized water, the third - low-mineralized water with the addition of iodide, cobalt, copper, manganese, molybdenum, zinc and fluoride. The latter group received low-mineralized water with the addition of the same elements, but ten times higher concentration. It was found that low-mineralized water affects the blood formation process. In animals treated with desalted water, the average hemoglobin content in the erythrocytes was 19% lower compared to rats that were given tap water. The differences in hemoglobin content were even higher compared with animals that received mineral water.

Recent epidemiological studies in Russia, conducted among groups of people living in areas with different salinity, suggest that low-mineralized drinking water can lead to hypertension and coronary heart disease, gastric and duodenal ulcers, chronic gastritis, goiter, pregnancy complications and a number of complications in newborns and infants, including jaundice, anemia, fractures and growth disorders. However, the researchers note that it remains unclear for them whether drinking water has such an impact on health, or whether it is all about the overall environmental situation in the country.

Answering this question by G. F. Lutaiconducted a large-scale cohort epidemiological study in the Ust-Ilimsk region of the Irkutsk region in Russia. The study focused on the incidence and physical development of 7658 adults, 562 children and 1582 pregnant women and their newborns in two water-supplied areas, differing in total salinity. The water in one of these areas had a total salt content of 134 mg / l, of which calcium was 18.7 mg / l, magnesium 4.9 mg / l, hydrocarbonates 86.4 mg / l. In another area, the total water salinity was 385 mg / l, of which calcium was 29.5 mg / l, magnesium 8.3 mg / l, and hydrogen carbonate 243.7 mg / l. The content of sulfates, chlorides, sodium, potassium, copper, zinc, manganese and molybdenum in water was also determined. The population of these two areas did not differ from each other in social and environmental conditions, the residence time in the respective areas,eating habits. Among the population of the area with less mineralized water, higher rates of goiter, hypertension, coronary heart disease, gastric ulcer and duodenal ulcer, chronic gastritis, cholecystitis and nephritis were found. Children living in the area showed a slower physical development, a manifestation of growth anomalies. Pregnant women are more likely to suffer from swelling and anemia. Newborns in this area were more prone to illness. The lowest incidence was observed in areas with bicarbonate water, with a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.Among the population of the area with less mineralized water, higher rates of goiter, hypertension, coronary heart disease, gastric ulcer and duodenal ulcer, chronic gastritis, cholecystitis and nephritis were found. Children living in the area showed a slower physical development, a manifestation of growth anomalies. Pregnant women are more likely to suffer from swelling and anemia. Newborns in this area were more prone to illness. The lowest incidence was observed in areas with bicarbonate water, with a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.Among the population of the area with less mineralized water, higher rates of goiter, hypertension, coronary heart disease, gastric ulcer and duodenal ulcer, chronic gastritis, cholecystitis and nephritis were found. Children living in the area showed a slower physical development, a manifestation of growth anomalies. Pregnant women are more likely to suffer from swelling and anemia. Newborns in this area were more prone to illness. The lowest incidence was observed in areas with bicarbonate water, with a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.cholecystitis and nephritis. Children living in the area showed a slower physical development, a manifestation of growth anomalies. Pregnant women are more likely to suffer from swelling and anemia. Newborns in this area were more prone to illness. The lowest incidence was observed in areas with bicarbonate water, with a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.cholecystitis and nephritis. Children living in the area showed a slower physical development, a manifestation of growth anomalies. Pregnant women are more likely to suffer from swelling and anemia. Newborns in this area were more prone to illness. The lowest incidence was observed in areas with bicarbonate water, with a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.having a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.having a total mineralization of about 400 mg / l and containing 30-90 mg / l of calcium and 17-35 mg / l of magnesium. The author came to the conclusion that such water can be considered physiologically optimal.

4. Elution of nutrients from food prepared in low-mineralized water.

It was found that when using softened water for cooking, there is a significant loss of food (meat, vegetables, cereals) of micro and macro elements. Up to 60% of magnesium and calcium, 66% of copper, 70% of manganese, 86% of cobalt are washed out of the products. On the other hand, when hard water is used for cooking, the losses of these elements are reduced.

Since most nutrients are ingested with food, the use of low-mineralized water for cooking and food processing can lead to a noticeable deficiency of some important micro and macro elements. The current menu of most people usually does not contain all the necessary elements in sufficient quantities, and therefore any factor that leads to the loss of basic mineral and nutrients in the cooking process, further aggravates the situation.

5. A possible increase in the intake of toxic substances.

Low-mineralized and especially demineralized water is extremely aggressive and is capable of leaching heavy metals and some organic substances from materials with which it contacts (pipes, fittings, storage tanks). In addition, calcium and magnesium contained in water, to some extent have an antitoxic effect. Their absence in drinking water, which also got into your tin cup by copper pipes, will easily lead to poisoning with heavy metals.

Among the eight cases of drinking water intoxication recorded in the United States in 1993-1994, there were three cases of lead poisoning in infants whose blood showed lead exceedances of 1.5, 3.7, and 4.2 times, respectively. In all three cases, lead was leached from lead-soldered joints in storage tanks for drinking reverse osmosis water, where baby food was diluted.

Calcium and, to a lesser extent, magnesium are known to have antitoxic activity. They prevent the absorption of heavy metal ions into the blood from the intestines, such as lead and cadmium, by competing for binding sites. Although this protective effect is limited, it cannot be discarded. At the same time, other toxic substances can react chemically with calcium ions, forming insoluble compounds and, thus, losing their toxic effect. The population in areas supplied with low-mineralized water may be at increased risk of toxic poisoning compared with the population in regions where ordinary hard water is used.

6. Possible bacterial contamination of low-mineralized water.

This item in the original article is a little far-fetched, but still. Any water is subject to bacterial contamination, which is why the pipelines keep the minimum residual concentration of disinfectants - for example, chlorine. It is known that reverse osmosis membranes are capable of removing practically all known bacteria from water. However, reverse osmosis water must also be disinfected and the residual concentration of the disinfectant in it must be kept in order to avoid secondary contamination. An illustrative example of an outbreak of typhoid fever caused by reverse osmosis treated water in Saudi Arabia in 1992. They decided to abandon the chlorination of reverse osmosis water, because, in theory, it was deliberately sterilized by reverse osmosis. The Czech National Institute of Public Health in Prague has experienced productsintended for contact with drinking water, and found, for example, that the pressure vessels of household reverse osmosis plants are susceptible to bacterial overgrowth.

1. 1980 (, ).

Drinking water with low mineralization leads to the leaching of salts from the body. Since side effects, such as a violation of water-salt metabolism, were observed not only in experiments with fully demineralized water, but also when using low-mineralized water with a total salt content in the range from 50 to 75 mg / l, the group of Yu. A. Rakhmanin in his report for WHO, it was recommended to set the lower bar for the total salinity of drinking water at 100 mg / l. The optimum salt content of drinking water, according to these recommendations, should be about 200-400 mg / l for chloride-sulphate water and 250-500 mg / l for bicarbonate water. The recommendations were based on extensive experimental studies conducted on rats, dogs and human volunteers. In the experiments used the Moscow tap water;desalinated water containing approximately 10 mg / l of salts; laboratory prepared water containing 50, 100, 250, 300, 500, 750, 1000 and 1500 mg / l of dissolved salts with the following ionic composition:

• among all chloride anions, 40%, hydrocarbonate anions 32%, sulfates 28%;
• among all sodium cations, 50%, calcium 38%, magnesium 12%.

A number of parameters have been studied: the dynamics of body weight, basal metabolism; enzyme activity; water-salt balance and its regulatory system; mineral content in tissues and body fluids; hematocrit and vasopressin activity. The final optimal mineralization was derived from data on the effects of water on the human body and animals, taking into account the organoleptic properties, the ability to quench thirst and the level of corrosivity with respect to the materials of water supply systems.

In addition to the level of total mineralization, this report substantiates the minimum calcium content in drinking water - at least 30 mg / l. This requirement was introduced after studying the critical effects resulting from hormonal changes in the metabolism of calcium and phosphorus and a decrease in bone mineralization with the use of calcium-free water. The report also recommends maintaining the content of bicarbonate anions at 30 mg / l, which contributes to maintaining acceptable organoleptic characteristics, reducing corrosivity and creating an equilibrium concentration for the recommended minimum calcium concentration.

2. Latest recommendations.

More recent studies have led to clarified requirements. Thus, in one of them, the effect of drinking water containing different concentrations of hardness salts on the health status of women aged 20 to 49 years in four cities of Southern Siberia was studied. Water in city A had the lowest content of these elements (3.0 mg / l calcium and 2.4 mg / l magnesium). The water in town B was harder (18.0 mg / l calcium and 5.0 mg / l magnesium). The highest hardness was observed in the cities of C (22.0 mg / l of calcium and 11.3 mg / l of magnesium) and D (45.0 mg / l of calcium and 26.2 mg / l of magnesium). In women living in cities A and B, diseases of the cardiovascular system (data obtained using an ECG), higher blood pressure, somatoform autonomic dysfunctions were more often diagnosed., headache, dizziness and osteoporosis (data obtained by X-ray absorptiometry ) compared with those in cities C and D. These results show that the minimum magnesium content in drinking water should be 10 mg / l, and the minimum calcium content can be reduced to 20 mg / l (compared with the WHO recommendations in 1980).

Based on the currently available data, various researchers have come up with such recommendations regarding the optimal hardness of drinking water:

but. magnesium - not less than 10 mg / l, optimally about 20-30 mg / l;
b. calcium - not less than 20 mg / l, optimally 40-80 mg / l;
at.their sum (total hardness) is 4–8 mEq / l.

At the same time, magnesium is limited from below by its effect on the cardiovascular system, and calcium - as a component of bones and teeth. The upper limit of the optimal range of hardness was established based on the fears of the possible influence of hard water on the occurrence of urolithiasis.

Effect of hard water on the formation of kidney stones

Under certain conditions, the dissolved substances contained in the urine can crystallize and deposit on the walls of the kidney cups and the pelvis, in the bladder, as well as in other organs of the urinary system.

By chemical composition, several types of urinary calculi are distinguished, however, due to the hardness of the water, phosphates and oxalates are of interest mainly. In case of violation of calcium-phosphorus metabolism or in the case of vitamin D hypervitaminosis, phosphate stones may form. The increased content of oxalic acid salts in the food - oxalates - can lead to the appearance of oxalate stones. Both oxalate and calcium phosphate are insoluble in water. By the way, there are many oxalates not only in sorrel, but also in chicory, parsley, and beetroot. And oxalates are synthesized by the body.

The effect of water hardness on urinary calculus formation is difficult to determine. Most of the studies evaluating the effect of water hardness on the emergence and development of urolithiasis (urolithiasis) use data from medical institutions. In this sense, a study by Schwartz et al. ^[3] , is significantly different in that all data were collected on an outpatient basis, while patients remained in their natural environment and were engaged in their usual activities. This paper presents the largest cohort of patients to date, which allows to evaluate the effect of water hardness on various components of urine.

Scientists have processed extensive material. US Environmental Protection Agency ( EPA)) provided information about the chemical composition of drinking water in the United States geographically. This information was combined with the national database of outpatients suffering from urolithiasis (it contains the patient's postal code, so the georeferencing was possible). Thus, 3270 outpatient patients with calcium stones were identified.

In most people's minds, increased water hardness is synonymous with an increased risk of developing urolithiasis (kidney stones are a special case of urolithiasis). The content of mineral substances, and especially calcium, in drinking water, apparently, is perceived by many people as a threat to health.

Despite these widespread concerns about water hardness, no research supports the suggestion that drinking hard water increases the risk of urinary calculi.

Sierakowski et al. examined 2,302 medical reports from inpatient hospitals scattered throughout the United States, and found that patients who lived in areas with hard water had a lower risk of urolithiasis. Similarly, in the cited paper ^[3], it was found that the hardness of drinking water is inversely proportional to the incidence of urolithiasis.

In the cited study, the number of episodes of urolithiasis was somewhat higher in patients living in areas with softer water, which is consistent with data from other authors, but contrary to public perception. It is known that in some cases, for example, in persons suffering from hypercalciuria , increased oral calcium intake can exacerbate the formation of urinary stones. In patients with hyperoxaluric calcium nephrolithiasisIncreased oral administration of calcium, on the contrary, can successfully inhibit the formation of stones by binding calcium salts of oxalic acid in the intestine and, thus, limiting the flow of oxalates into the urinary system. Calcium intake from drinking water can potentially have an inhibitory effect on the formation of calcium urinary calculi in some patients and promote the formation of stones in others. This theory was tested in the work of Curhan et al., During which the effect of calcium intake was evaluated in 505 patients with repeated stone formation. After 4 years of follow-up in the group of patients taking calcium, the smallest number of episodes of the appearance of urinary stones was noted. The researchers concluded that high calcium intake with food reduces the risk of symptomatic urolithiasis.

Despite public concern about potential lithogenesis of hard tap water, existing scientific evidence suggests that there is no connection between water hardness and the prevalence of stone formation in urine. It seems that there is a correlation between water hardness and the level of calcium, citrate and magnesium in the urine, but the significance of this is unknown.

By the way, the author ^[3] gives an interesting comparison: the consumption of one glass of milk can be equivalent to two liters of tap water in terms of calcium content. Thus, according to the United States Department of Agriculture ( USDA ), 100 g of milk contains 125 mg of calcium ^[4] . The same amount of city water contains only about 4-10 mg of calcium.

Conclusion

Drinking water should contain minimal concentrations of certain essential minerals. Unfortunately, the beneficial properties of drinking water have always been given too little attention. The main focus was on the toxicity of untreated water. The results of recent studies aimed at determining the optimal mineral composition of drinking water should be heard not only by public and private structures responsible for water supply to entire cities, but also by ordinary people abusing water treatment systems at home.

Drinking water produced by desalination plants on an industrial scale is usually remineralized, but at home the mineralization of reverse osmosis water is usually not performed. However, even with the salinity of desalinated waters, their chemical composition may remain unsatisfactory from the point of view of the needs of the organism. Yes, calcium salts can be added to water, but it will not contain other essential trace elements - fluorine, potassium, iodine. In addition, desalinated water is mineralized more for technical reasons - to reduce its corrosiveness, and the importance of substances dissolved in water for human health is usually not considered. None of the methods used for remineralizing desalinated water can be considered optimal, since only a very narrow set of salts is added to the water.

The effect of hard water on the formation of kidney stones is not scientifically confirmed. There are concerns that an increased intake of oxalic acid salts or phosphates together with calcium may lead to crystallization of insoluble calcium salts of phosphoric or oxalic acids in the urinary system, but the organism of a healthy person, according to existing scientific data, is not subject to such a risk. At risk may be persons suffering from kidney disease, vitamin D hypervitaminosis, impaired calcium-phosphorus, oxalate, citrate metabolism, or eating significant amounts of oxalic acid salts. It has been established, for example, that a healthy organism, without any consequences for itself, is capable of processing up to 50 mg of oxalates per 100 g of food, but only spinach contains oxalates of 750 mg / 100 g,therefore, vegetarians may be at risk.

In general, demineralized water is no less harmful than wastewater, and in the XXI century it is high time to move away from rationing water quality indicators only from above. Now it is necessary to establish also the lower boundaries of the content of mineral substances in drinking water. Physiologically, only a narrow corridor of concentrations and composition of drinking water is optimal. The information currently available on this issue can be presented in tabular form.

Table 1. Optimum mineralization of drinking water

Element	Units	Minimum content	Optimal level	Maximum level, SanPiN 2.1.4.1074-01 or * WHO recommendation
Total mineralization	mg / l	100	250-500 for bicarbonate waters 200-400 for chloride-sulphate waters	1000
Calcium	mg / l	20	40-80	-
Magnesium	mg / l	ten	20-30	-
Sodium	mg / l	-	-	200
Alkalinity	mg-eq / l	-	-	6.5 *
Bromine	mg / l	-	0.01	0.2
Boron	mg / l	-	0.5	0.5
Hydrocarbonate	mg / l	-	thirty	-
Fluorides	mg / l	0.5	0.7-1.2	1.2

Literature

1. F. Kozisek, “Health risks from drinking demineralized water”
2. Wikipedia, lethal dose of water
3. BF Schwartz, “Calcium nephrolithiasis: effect of water hardness on urinary electrolytes”
4. USDA, milk chemical composition