If we want to use hard water in textile dye processing first off all we need to remove the hardness of water. There are two types of hardness (a) Temporary hardness, (b) permanent hardness.

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 

Permanent Hardness:   

CaSO4 + Na2CO3 → CaCO3+ Na2SO4    

       2. MgSO4 + Na2CO3 → MgCO3+ Na2SO4  

           MgCO3 + Ca(OH)2 → Mg(OH)2 + CaCO3