raw water is termed hard when it contains dissolved salts of calcium & magnesium. Temporary, alkaline or carbonates of calcium & magnesium, permanent, non alkaline or non carbonate hardness is caused by dissolved chlorides, sulphates or nitrates of calcium & magnesium, softner remove hardness in water. The softening process consists of passing raw water containing hardness through a bed of cation resin in sodium form. The hardness ions ca & mg are taken up by resin and in exchange sodium ions are relinquished from the resin. Raw water will continue to get softened till the resin gets exhausted. Bringing back the resin to it original form is called regeneration. Softener resin is regenerated by sodium chloride of 1015% concentration.