Dyes are affected by metal ions Calcium and Magnesium present in high concentration in the hard water. These metal ions cause hydrolysis of dyes to form insoluble complexes. This is one of the major reason for shade variation. Use of water softener is helpful in chelating metal ions thus improving dye solubility and performance.
There are two types of water hardness.
(1) Temporary hardness , (2) Permanent hardness


(1) Temporary hardness : Temporary hardness is caused by calcium and/or magnesium carbonate. Temporary hardness can be removed simply by boiling the water or by taking the help of the following reactions:

Ca(HCO3)+Ca(OH)2→2CaCO3↓+2H2O

Mg(HCO3)2+2Ca(OH)2→2MgCO3+2H2O

MgCO3+Ca(OH)2→Mg(OH)2+CaCO3

(2) Permanent hardness : Permanent hardness is caused by calcium or magnesium sulphate. Permanent hardness cannot be removed by boiling but can often be removed by chemical treatment (see below ).

CaSO4+Na2CO3→CaCO3+Na2SO4

MgSO4+Na2CO3→MgCO3+Na2SO4

MgCO3+Ca(OH)2→Mg(OH)2+CaCO3