Low intake of dietary magnesium in typical western diet is associated with magnesium deficiency and its related diseases. Americans are falling short of dietary intake of magnesium by 27 and 52 mg / day for men and women respectively. Water supplies only 6-7 % of the daily requirement of magnesium. Magnesium deficiency is common in normal and hospitalized people (2% & 26% respectively); while critically sick patients have hypomagnesaemia up to 60 %. Hypomagnesaemia influence the prognosis of the disease resulting in high mortality in severely sick and hypomagnesaemic patients, as compared to other hospitalized patients. Magnesium in hard water is known for its cardio protective effect especially against sudden cardiac death by preventing malignant arrhythmias and coronary vasospasm. Waterborne magnesium is also known for its protective effect on diabetes, metabolic syndrome, hypertension, stroke, insulin resistance, preeclampsia, and other chronic diseases. It is so much effective that even a small amount (6 mg / l) can prevent the cardiovascular mortality by 10% (a disproportionate response). Hard water supplies other micronutrients like, calcium, zinc, iodine etc. and it also protects the body against other harmful chemicals of water like, cadmium, aluminum, beryllium, mercury, and nickel. Demineralized water produced through reverse osmosis process remove 93-97% of calcium and magnesium. Such water is stripped of its beneficial elements and produce magnesium deficiency if consumed for prolonged period.