The various kinds of salts depend on the geological formations through which the water was flowed. These salts are mainly the carbonates, hydrogen carbonates or bi-carbonates, sulphates, chlorides of calcium and magnesium. Although calcium and magnesium carbonates in limestone are relatively insoluble in water. So in this reasons, water hardness can be devided into two ways. They are-
1. Temporary hardness: Temporary hardness is caused by calcium or magnesium hydrogen carbonate.
2.Permanent hardness : Permanent hardness is caused by calcium or magnesium sulphate.
Temporary hardness:
1. Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 ↓ +2H2O
2. Mg(HCO3)2 + 2Ca(OH)2 → 2MgCO3 +2H2O
MgCO3 + Ca(OH)2 → Mg(OH)2 + CaCO3