WHO Meeting of Experts on the Possible Protective Effect of Hard Water Against Cardiovascular Disease by WHO

Both calcium and magnesium are essential to human health. Inadequate intake of either nutrient can impair health. Standards for recommended daily intakes of each element have been set at national and international levels. Food is the principal source of both calcium and magnesium. Dairy products are the richest sources of dietary calcium, contributing over 50% of the total calcium in many diets. Some plant foods, including legumes, green leafy vegetables and broccoli, can also contribute to dietary calcium, but the content is lower than in dairy products, and the bioavailability calcium in plant foods can be low if the concentration of oxalate or phytate is high. Dietary sources of magnesium are more varied; dairy products, vegetables, grain, fruits and nuts are important contributors. Individuals vary considerably in their needs for and consumption of these elements. Available evidence suggests that, because of food habits, many people in most countries fail to obtain from their diets the recommended intakes of one or both of these nutrients. While the concentrations of calcium and magnesium in drinking-water vary markedly from one supply to another, mineral-rich drinking-waters may provide substantial contributions to total intakes of these nutrients in some populations or population subgroups.

Link : http://www.who.int/water_sanitation_health/gdwqrevision/cardiofullreport.pdf