Softening:
Water is considered to be hard if it does not form leather readily with the soap. Hardness of water is due to presence of calcium and magnesium salt. The greater the concentration of these salts in the water, the harder the water is. It is expressed in mg/l or meq/l as CaCO3. There are two types of hardness:
(a) Temporary (Carbonate Hardness).
(b) Permanent (Non-carbonate Hardness).
The temporary or carbonate hardness, which is caused by carbonates and bicarbonates of calcium and magnesium can be removed by boiling or by adding lime whereas the permanent or non-carbonate hardness, which is caused by the sulphates, chlorides and nitrates of calcium and magnesium are removed by special methods. The reduction or removal of hardness from water is known as water softening. The advantages of softening lies chiefly in the reduction of soap consumption, lowered cost in maintaining plumbing fixtures and improved taste of food preparations.