Water Softening Method:

Normally following two methods are used for softening of the water:

(a) Chemical precipitation.

(b) Ion Exchange.

Chemical Precipitation

In chemical precipitation, lime (Ca (OH)₂) and soda (Na₂CO₃) are added together or separately in water to reduce/remove the hardness. Lime and soda converts hardness causing compound (calcium and magnesium salts) to insoluble precipitates; which are settled out and supernatant liquid is filtered. This method of softening also achieves substantial removal of such constituents as iron and manganese, which may be present in high concentrations in ground water. This method is used particularly for water with initial hardness (greater than 500 mg/l) and suitable for waters containing turbidity, color and iron salts because these have a tendency to inactivate the ion-exchange bed, by a coating on the granules. Lime-soda softening cannot, however, reduce the hardness to values less than 40 mg/l while ion-exchange softening can produce zero-hardness water.