hard water

Hard water is water containing calcium and magnesium ions and hence forming scum with soap and depositing scale in boilers, pipes, and kettles. Temporary hardness is due to calcium and magnesium bicarbonate (hydrogencarbonate); it is removed by boiling, which precipitates the carbonates. Permanent hardness (unaffected by boiling) is due to the sulfates. Hard water may be softened by precipitation of the metal using calcium hydroxide and sodium carbonate, followed by sodium phosphate; or, by a zeolite or ion-exchange column, which exchanges the calcium and magnesium ions for sodium ions.