In biology classes we learn that osmosis describes the movement of water across a membrane impermeable to organic solutes with large molecules, such as polysaccharides, while permeable to water and small, uncharged solutes (e.g. selectively permeable membrane) from an area of low solute concentration to an area of high solute concentration. When a cell is placed into a hypotonic solution (e.g. solute concentration lower than intracellular) the net movement of water is into the cell through its selectively permeable membrane in order to equalize solute concentration. If water molecules continue to diffuse into the cell, it will cause the cell to swell, up to the point that cell-death may occur. Therefore it would be life-threatening for humans if salt-free water would be injected directly into a vein.
For this very reason there might be the wide-spread belief that salt-free water is harmful to health. In spite of this the World Health Organization (WHO) declares drinking salt-free water as safe. Just as there are countries were distilled water is sold as bottled drinking water. In addition salt-free water is used as drinking water in the most arid areas which do not have sufficient freshwater, by distilling seawater. This discrepancy of cell physiology learned in biology lessons and real world human physiology has two main reasons.
Little of our daily consumption of minerals and ions comes from our drinking water, for the most part they come from the food we eat. For example the recommended daily sodium allowance is 2000–3000 mg whereas mineral waters (e.g. Evian) contain about 5 mg of sodium per liter. Thus, an individual would have to drink 500 liters of Evian to achieve the recommended daily sodium allowance. Or an individual with sufficient fluid intake, which means approximately 2 liters per day would absorb the maximum of 0.5 % of their daily sodium requirement by drinking mineral water.
The capacity of the kidney to dilute urine down to a low solute concentration (Osmolarity) prevents the body from retaining free water. Dr. Daniel Fuster Nephrologist at the University Hospital of Bern, Switzerland puts the drinking of salt-free water into perspective.
“A human being on a regular diet needs to excrete about 800–1000 mosmmoles of solutes a day, of which about 50 % are salts and 50 % urea. therefore somebody with normal renal function on a regular diet can dilute the urine down to about 50 mosmoles/l, as a result one can excrete the daily solutes in 16–20 liters of urine and not retain free water. Otherwise put, a person with normal kidney function could drink 16–20 liters of salt-free water a day.”
Thus, the drinking of large amounts of salt-free Sanakvo water, assuming normal diet and normal renal function, is absolutely harmless.
Nonetheless, irrational drinking habits (e.g. water drinking contests, in which individuals attempt to consume large amounts of water) or intensive exercise during which electrolytes are not properly replenished, yet excessive amounts of fluid are still consumed, push the body’s regulatory system to its limit and result in water intoxication. Though this is non-exclusive for salt-free Sanakvo water and can also occur with normal drinking water (e.g. mineral water). In general water intoxication occurs at a drinking level far higher than the medically recommended drinking amount of 1–2 liters per day and can be prevented if a person's intake of water does not grossly exceed his or her losses.
For an individual it is perfectly fine to drink Sanakvo salt-free water when ingested in normal amounts.
2011-02-01 P. H.