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.

(a) To remove temporary hardness we need to boil the hard water.

(b) To remove permanent hardness we need to do reaction the water with Sodium carbonate and Calcium Hydroxide.

Temporary hardness:

1. Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ ↓ +2H₂O

2. Mg(HCO₃)₂ + 2Ca(OH)₂ → 2MgCO₃ +2H₂O

3. MgCO₃ + Ca(OH)₂ → Mg(OH)₂ + CaCO₃

Permanent Hardness:  

CaSO4 + Na2CO3 → CaCO3+ Na2SO4   

MgSO4 + Na2CO3 → MgCO3+ Na2SO4  

MgCO3 + Ca(OH)2 → Mg(OH)2 +  CaCO3