CWQA Position Statement
Sodium in Drinking Water
CWQA Position:
The Canadian Water Quality Association believes that based on the best available evidence, softened water makes no significant contribution to hypertension in a normal health population. Those few sodium sensitive individuals who are on a strict 500 mg/day (sodium) diet should avoid soft water intake. However, in these cases the advantages of soft water washing, bathing and water heater/pipe protection can still be realized using the options of a hard water bypass or the installation of point-of-use sodium removal devices such as reverse osmosis or distillation systems.
Background:
Common table salt or as it is known by its chemical name, sodium chloride, is essential to human nutrition. In water, salt separates into two ions: sodium and chloride. The sodium ion regulates the osmotic pressure of the blood plasma assuring the proper blood volume and also controls the amount of fluid around the body cells. It is also necessary in the contraction of body muscles particularly, the muscles of the heart. The chloride ion helps to maintain the proper concentrations of various body chemicals. Sodium chloride is essential in the formation of the stomach acids necessary for the digestive processes2.
A minimum recommended daily intake of sodium in the human body has not been authoritatively established. The Committee of Sodium Restricted Diets and the Food and Nutrition board of the National Research Council (U.S.) indicated that the "habitual total (daily) intake (of sodium) of 3,000 to 4,000 milligrams..." The publication also indicated that a mild sodium restricted diet consists of less than 2,0001 milligrams/day. However, there is a very special risk group of people who are highly sensitive to sodium and must be on a severe sodium restricted diet of 500 milligrams/day. The National Research Council (U.S.) has stated, "Adverse health effects may be anticipated with sodium concentrations in water greater that 20 mg/I only for that special risk group restricted to total sodium intake of 500 mg/day, because intake from food cannot be reduced feasibly to less than 440 mg/day1." The document goes on to say that this low sodium diet is virtually impossible without hospitalization.
Researchers over the past few years have attempted to correlate a relationship between natural soft water and cardiovascular disease. These epidemiological studies have been inconclusive. Naturally soft water contains a very small amount of other minerals such as sodium. Artificially softened water has never been implicated in these studies. An U.S. EPA sponsored symposium "Conference on Inorganics in Drinking Water and Cardiovascular Disease" was held in 1984 at the University of Massachusetts (Canadians participating). A summary of this worldwide meeting indicated unequivocally that there was no causal relationship between softened drinking water and cardiovascular disease. Governments have suggested a guidance level3 of 20 mg/I in drinking water for the high risk population under severe sodium restrictions (500 mg/day)
The effect of sodium alone on hypertension has not been established. For example, the results of five recent important independent studies4 on both humans and laboratory animals suggests that sodium may be a factor in hypertension unless it is associated with chloride ion. In the water softening process, hardness ions (calcium and magnesium) are exchanged onto the resin bed for sodium ions which enter the water supply. There is no addition of chloride ions. Most of the sodium is in the form of sodium bicarbonate which according to these studies would have no effect on hypertension.
Regardless of these recent developments, the amount of sodium obtained from drinking softened water is insignificant compared to the sodium ingested in the normal diet. The amount of sodium introduced to a litre of drinking water by softening very hard 18 grains per gallon water is approximately 140 milligrams. If an individual consumes one litre of water per day, the sodium intake is less than 5% of the average daily intake. It is equivalent approximately to the sodium contained in a normal slice of white bread5 and this intake may be small compared to other liquids that an individual may ingest. In addition, an 8 oz. serving of this water would contain 35 milligrams considered "very low sodium" in the U.S. FDA in their new regulation on nutrition labelling of sodium content6.
Summary:
The Canadian Water Quality Association believes that currently available information on softened water and health leads to a conclusion that softened water makes no significant contribution to hypertension in a normal healthy population. However, the CWQA will continue to maintain a close surveillance on all developments on the subject of softened water and health in order to provide customers with the best available current information. CWQA will also continue to interact with government and health organizations concerning the water softening industry and human health.
References:
1. National Academy of Sciences, The National Research Council, Drinking Water and Health. 1977, p.436.
2. National Academy of Sciences, The National Research Council, Drinking Water and Health, 1977, p.402.
3. Federal Register. Vol.45, No. 168, August27, 1980, p.57336.
4. Morgan, T.O., The Effect of Potassium and Bicarbonate Ions on the Rise in Blood Pressure Caused by Sodium Chloride. Clinical Science (1982) 63, pp.407s-409s.
Kurtz, Theodore W., and R. Curtis Morris, Jr., Dietary Chloride as a Determinant of "Sodium-Dependent" Hhypertension. Science, Vol. 222, December 9,1983, pp. 1139-1141.
Husted, Frederick C., Karl D. Noiph and John F. Maher, NaCLO3 and NaCL Tolerance in Chronic Renal Failure. The Journal of Clinical Investigation, Volume 56, August, 1975, pp.41 4-419.
Kotchen, Theodore A., M.D., et al., Effects of Chloride on Renin and Blood Pressure Responses to Sodium Chloride. Annals of Internal Medicine, 1983 (Part 2), pp. 817-822.
McCarron, David A., Cynthia D. Morris and Clarice Cole, Dietary Calcium in Human Hypertension, Science, Vol. 217, July 16, 1982, PP. 267-269.
5.Water Quality Association, Easy-to-Use Guide to Sodium in Food. Medicine and Water, R-8.
6.Federal Register. Vol. 49, No. 76, April 18, 1984, p.15518.
7.Federal Register, Vol, 53, No. 14, January 22,1988, p. 1892.
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