Calcium and magnesium in China's public drinking water and their daily estimated average requirements.

Calcium (Ca) and magnesium (Mg) in drinking water and the relevant health effects have been ignored for too long. This study aims to reveal the concentrations, spatial distributions, origins and contributions to the daily estimated average requirements of Ca and Mg in public drinking water. Using hydrochemical data of collected samples of public drinking water in 314 cities across China, the contributions of Ca and Mg intakes from public drinking water to their daily estimated average requirements (EARs) were assessed. And the significance of Ca/Mg ratio and total hardness (TH) was evaluated as well. The Ca and Mg concentrations of the samples were in the range of 2.5-155.1 mg/L and 0.2-81.9 mg/L, with an average of 40.4 mg/L and 12.4 mg/L, respectively. There exist obvious differences in Ca and Mg concentrations in different regions, under the impact of climate conditions and water-rock interactions. The intake of Ca via the consumption of public drinking water for adults may be twice as much as that for other age groups. In cities with high Ca levels in public drinking water, the Ca contributions to EAR could reach up to 51.59% for adults. By contrast, Mg in drinking water is an important and even the main pathway to ingest Mg for infants and children. Therefore, public drinking water is critical for Ca and Mg intake among urban residents of China. Besides, attention should be paid to the health effects of high Ca/Mg ratio and low TH in public drinking water, especially in southern China. This research is the first systematic and comprehensive national scale study of Ca and Mg in public drinking water and can provide an important reference to improve healthy public drinking water standards around the world.