Water is generally clear and transparent but minerals and the concentration of chemicals make it soft or hard water. Soft water produces a good lather with soap and hard water does not. Hard water contains chlorides and sulphides of magnesium and calcium. Therefore, water dissolves many salts of divalent cations like Mg2+, Ca2+, and anions like Cl-, SO42-, HCO3-. Hardness is of two types.
Temporary hardness is due to the presence of bicarbonates of calcium and magnesium. Permanent hardness is due to sulphates and chlorides. Temporary hardness can be treated by boiling and Clark’s method. Permanent hardness can be treated by washing soda and by using sodium zeolite.