In the United States variations from state to state in death rates from cardiovascular diseases have been unexplained on dietary, racial, or social bases. One variable environmental influence to which all persons are exposed is potable water. Statistical analyses of water hardness and death rates from all causes, cardiovascular diseases, coronary heart disease, and noncardiovascular diseases, showed highly significant correlations for all but noncardiovascular causes. Similar relationships were demonstrated for caucasoid men, aged 45 to 64 years, by state and, in the case of coronary disease, in the 163 largest cities. Of 21 constituents of finished municipal water in each city, highly significant correlations were found for magnesium, calcium, bicarbonate, sulfate, fluoride, dissolved solids, specific conductance, and pH. In all cases correlations were negative, i. e., softer water was associated with higher death rates. Some factor either present in hard water or missing or entering in soft water appears to affect death rates from degenerative cardiovascular disease.