Water hardness and mortality in the Netherlands.

In 1975 central water softening was discouraged by the Public Health Council because of the statistical negative association found in 23 communities between the hardness of drinking water and death rate from Ischemic Heart Disease (I.H.D.) over the period 1958-1970. Further studies were carried out during the last decade by a specially assigned interdisciplinary Working Group of the Health Aspects of Central Water Softening. Recent studies showed that the release of metals (Pb and Cu) from household water distribution pipes was positively correlated with water calcium. Furthermore a significant negative correlation was found between hardness and pH for these types of water. The hypothesis that the Ca and Mg deficiency in areas with soft drinking water increases the risk of I.H.D. death rate was supported by the finding that food looses more Ca and Mg when it is cooked in soft water as compared to cooking in hard water. In contrast with earlier statistical investigations no significant relations were found over the period 1970-1977 between I.H.D. mortality and hardness of drinking water in 30 municipalities. The disappearance of the statistical relation could not be attributed to changes in water hardness. However, investigation of a group of 17 municipalities of which mortality and water quality data are known for three periods, 1958-1962, 1965-1970 and 1971-1977, showed that the inverse statistical relation between I.H.D. mortality and water hardness still existed but with decreasing significance of correlation coefficients. The provisional conclusion of the Working Group is that other factors than water hardness overrule to a large extent the potential effect on I.H.D. mortality. Central water softening down to 2-3 meq/l Ca probably will have no observable effect on mortality. Other studies are still continuing. In 1981 a final report will be presented to the Minister of Health and Environmental Protection.