The hypothesis that the hardness of drinking water has a causal role in the development of cardiovascular disease will be strengthened if it can be demonstrated that elements in drinking water find their way into human tissues in significant amounts. For biologically important metals, the evidence is reviewed for a relationship of tissue levels to levels in drinking water. Hard water can contribute significantly to daily magnesium intake. Residents of hard-water areas may have raised levels of magnesium in coronary arteries, bone, and myocardial tissue. Lead levels in bone and in blood have been shown to be elevated in individuals living in homes with lead plumbing and soft water. Cadmium intake from water is probably small compared to that from other sources, and there is no convincing evidence of alteration in human tissue levels via drinking water cadmium. Human zinc and copper tissue levels are of interest but have not been adequately studied in relation to drinking water levels.