Despite the decreasing trend of cardiovascular disease (CVD) mortality, it is still the major cause of death in industrialized countries. CVDs are a major public health concern also in developing countries. Geographical variation in occurrence of coronary heart disease (CHD) between different countries and also within countries is well established but reasons for this variation are ambiguous and not satisfactorily explained by the known CHD risk factors. Major risk factors, such as hypertension, smoking, dyslipidemia, diabetes, physical inactivity, and obesity, give only partial explanation for geographical variation of CHD. Among men, the classical risk factors explained less than 25% of geographical variance of all CVD and CHD mortality between populations. The protective role of magnesium and calcium in drinking water against CVDs has been discussed since it was first reported 50 years ago. During past decades, several epidemiological studies have reported the lower heart disease risk in areas with hard water with high levels of magnesium or calcium. Magnesium and calcium, the principal components of water hardness, are both essential nutrients for human health. The available information supports the hypothesis that intake of hard water, especially rich in magnesium, decreases the risk of CVD. At present, there are no international regulations – either minimum levels or maximum limits – for magnesium, calcium, or water hardness.