BACKGROUND AND OBJECTIVE: Calcium (Ca(2+)) intake through diet is mainly obtained from dairy products. However, there are other sources of Ca(2+), such as water, which can significantly contribute to its intake. Moreover, water also contains other minerals, such as magnesium (Mg(2+)) and sodium (Na(+)), with potential implications for health. Thus, Mg(2+) has been associated with a reduction of sudden death, whereas Na(+) contributes to the occurrence of hypertension. The rise in the consumption of bottled water in the general population clearly indicates the necessity of knowing the possible effects on health. Indeed, there may be a great variation in the content of these minerals depending on the type of water. METHODS: We obtained the mineral content of Ca(2+), Mg(2+) y Na(+) from tap water of 492 Spanish towns and cities (through data given by autonomous communities, city/town halls or municipal water companies) and from 182 commercially available bottled waters (122 available in Spain, 60 available in Europe). The results were compared with the recommended dietary intake of these minerals. RESULTS: There is a great variation in the mineral content among the different bottled waters and also among tap waters. Thus, among bottled waters in our country the Ca(2+) concentration ranges between 0.5-672 mg/l; 16% of these waters had a concentration > 100 mg/l and only two > 300 mg/l; some European waters showed high concentrations of Ca(2+) (459-575 mg/l); Na+ concentrations ranged between 0.1-2.000 mg/l, and Mg(2+) between 0.1-128. In tap water Ca2+ concentrations ranged between 0-337 mg/l, Na+ between 1-332 mg/l, and Mg(2+) between 0.3-315 mg/l. In 33.4% of the analysed tap waters the Ca(2+) concentration was > 100 mg/l, in 4 of them it was > 200 mg/l. CONCLUSIONS: Water, even bottled water or tap water, has a great variability in the concentrations of Ca(2+), Mg(2+) and Na(+). In some occasions, water may even supply the minimum recommended intake of Ca(2+) and Mg(2+) and can exceed the Na+ content. These data should be considered when selecting one for consumption.