Softening of water is recommended when hardness exceeds

HARDNESS OF WATER Hardness may be defined as the soap destroying power of water. The consumer considers water hard if large amounts of soap are required to produce lather. The hardness in water is caused mainly by four dissolved compounds. These are (1) Calcium bicarbonate (2) Magnesium bicarbonate (3) Calcium sulphate, (4) Magnesium sulphate. The presence of any one of these compounds produces hardness. There are others which are of less impoance. Chlorides and nitrates of calcium and magnesium can also cause hardness but they occur generally in small amounts. Iron, manganese and aluminium compounds also cause hardness, but as they generally are present in such small amounts, it is customary not to consider them in connection with hardness. Drinking water should be moderately hard. Softening Of water is recommended when the hardness exceeds 3 mEq/l (150 mg per litre). Ref: Park 25th edition Pgno : 763