The first undertaking of the Safe Drinking Water Committee of the National Academy of Sciences was the identification of substances and their concentrations in the nation's water supply that might pose risks to the public health. This report, on the other hand, identifies and discusses substances found in drinking water which may have nutritional significance. The substances addressed include calcium, magnesium, phosphorus, fluoride, sodium, potassium, chloride, iodine, iron, copper, zinc, selenium, manganese, arsenic, nickel, vanadium, silicon, molybdenum, and chromium. For each substance, data on occurrence in food and water are reviewed, nutritional requirements, toxicity versus essential levels, and the contribution from drinking water are assessed. Recommendations are made regarding the appropriateness of controlling these substances in drinking water.