Malformations of central nervous system and softness of local water supplies.

The mean annual prevalence at birth of congenital malformations of the central nervous system for the three years 1964-6 in 48 local authority areas in South Wales was negatively correlated (r = -0.402, P<0.01) with estimates of the mean total hardness of the related water supplies.The mean annual perinatal mortality rate from anencephalus for the five years 1963-7 in 58 county boroughs in England and Wales was also negatively correlated with estimates of the mean total hardness (r = -0.220, P>0.05) and calcium content (r = -0.289, P<0.05) of the related water supplies.It is concluded that the relationship between these associations may well be secondary. Analytical epidemiological studies of the association are called for.