In the United States, hardness (mostly magnesium and calcium) is removed from drinking water to prevent scaling of pipes and consumption of soap. Several studies indicate magnesium and calcium may be protective against heart disease. Removing hardness by ion exchange results in an increase in sodium concentration. Sodium is a well established risk factor for hypertension and resulting ischemic heart disease. An ecologic trends study of community mortality rates of heart disease in Iowa will be conducted to test three hypotheses: 1) mortality rates of heart disease are elevated in communities using ion exchange softening treatment; 2) communities using lime softening treatment have lower mortality rates of heart disease compared to communities using ion exchange; and 3) drinking water hardness may be protective against heart disease. Linkage of existing health outcome and municipal water quality databases maintained by the State Health Registry of Iowa and CHEEC will be a main component of this study. Significant differences in mortality rates of heart disease by type of softening treatments would indicate that more in-depth studies are warranted. Technical Report Available.