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water softening[′wȯd·ər ‚sȯf·ə·niŋ]
the reduction, to specified limits, of the hardness of natural water by the removal of calcium and magnesium salts from the water. In water purification, precipitation and cation-exchange methods are the primary means of water softening. A thermal method is also used in which the water is heated to a temperature above 100°C in order to remove completely the salts that cause carbonate hardness. (See alsoWATER TREATMENT.)
The process of removing divalent cations, usually calcium or magnesium, from water. When a sample of water contains more than 120 mg of these ions per liter (0.016 oz/gal), expressed in terms of calcium carbonate (CaCO3), it is generally classified as a hard water. Hard waters are frequently unsuitable for many industrial and domestic purposes because of their soap-destroying power and tendency to form scale in equipment such as boilers, pipelines, and engine jackets. Therefore it is necessary to treat the water either to remove or to alter the constituents for it to be fit for the proposed use.
The principal water-softening processes are precipitation, cation exchange, electrical methods, or combinations of these. The factors to be considered in the choice of a softening process include the raw-water quality, the end use of softened water, the cost of softening chemicals, and the ways and costs of disposing of waste streams. See Water treatment