Calcium comes from rocks, especially gypsum and limestone. In most water, calcium ions are the predominant cations.
Calcium must be removed from water used in many industrial processes, and an entire industry is based around removing hardness from residential water. As hardness, calcium can cause severe damage to residential plumbing pipes and fixtures.
Calcium is more a plumbing issue than a health issue, though some schools of thought have it that lack of calcium as in distilled or reverse osmosis treated water is not healthful. There is no convincing evidence to support this view, or for that matter the opposing view that water with calcium is harmful to health.
Calcium Removal - Calcium is readily removed from water by a simple sodium form ion exchanger, commonly known as a water softener. Reverse osmosis removes 95% to 98%, but removal of hardness usually causes scaling of RO membranes. Calcium can also be removed by deionizers (hydrogen form cation exchangers), dialysis, distillation and ultrafiltration.
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