Little is known about the bioavailability of calcium in water and various beverages. Some mineral waters contain large amounts of calcium that could compensate for insufficient consumption of dairy products. The fractional intestinal absorption of calcium (FCA) was measured in 12 healthy adult volunteers, using a trace dose of radiocalcium and 200 mg of calcium carrier, part of which was calcium contained in mineral water. Measurements were performed in fasting subjects consuming a standard breakfast. In all the subjects, three mineral waters with a calcium concentration of 10.4, 78, and 467 mg/l, respectively, were tested. Calcium absorption occurred with the same kinetics for each of the mineral waters tested, and within 2 h of the oral dose, equilibrium was reached between absorbed calcium and calcium remaining in the gastrointestinal tract, which resulted in a constant FCA value. This level comprising between 34.1 and 37.0% was independent of the daily calcium consumption and the chemical content of the mineral water. In conclusion, calcium contained in mineral waters in available for intestinal absorption. In a given normal subject, the only rate-limiting factor for FCA is the amount of total calcium given with foods and drinks. Mineral waters containing calcium are recommended as a supplemental source of calcium to achieve optimal calcium requirements, especially in aged people with lactose intolerance.