Water hardness means having the metal ions present in water which causes some issues in textile processing and others. Usually, the metal ions are  Calcium ions and Magnesium ions. There are two types of water hardness.
(1) Temporary hardness, (2) Permanent hardness

(1) Temporary hardness: The calcium/Magnesium carbonate causes temporary hardness. Temporary hardness can be removed by simply boiling or by the following reaction

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: The Calcium/Magnesium sulphate causes permanent hardness. Permanent hardness can be removed by chemical treatment.

CaSO4+Na2CO3→CaCO3+Na2SO4

MgSO4+Na2CO3→MgCO3+Na2SO4

MgCO3+Ca(OH)2→Mg(OH)2+CaCO3