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:   

1. CaSO₄ + Na₂CO₃ → CaCO₃+ Na₂SO₄    
2. MgSO₄ + Na₂CO₃ → MgCO₃+ Na₂SO₄   
   
3. MgCO₃ + Ca(OH)₂ → Mg(OH)₂ +  CaCO₃