Hard water has high content of mineral. When water percolates through the deposits of chalk and limestone composed of magnesium and calcium carbonates, it is produced. It does not lather with soap, so for laundry purposes it is not appropriate.
The process in which hard water containing Ca2+ is filtered through sand named zeolite is called Permutit process. Permutit is a zeolite of an artificial source. It is orthosilicate of sodium aluminium compound with chemical formula Na2Al2Si2O8.xH2O. Chemically, it is hydrated sodium aluminium orthosilicate.
In a high cylindrical vessel filled with gravel sand and permutti, the water softening procedure is done. Via an inlet, durable water is added. The water enters the vessel’s bottom. The gravel layer carries out the removal of impurities. It then comes into contact with permutit, which in tank water substitutes Mg2+ and Ca2+ ions into Na+ ions.
The chemical reaction is expressed as shown below.
Na2X + (Ca2+ or Mg2+) → CaX or MgX + 2Na+
Where X = Na2Al2Si2O8.xH2O.