Demineralisation is the Process of removing the mineral salts from water by ion-exchange. Impurities that remains dissolved in water dissociate to form positive and negative charged particles known as ions. These impurities or compounds are called electrolytes. Generally, all natural water has electrolytes in varying concentrations. An ion-exchange vessel holds ion-exchange resin of the required type through which water is allowed to pass. The selective ions in the water are exchanged with ions or radicals loosely held by the resin. In this way, the water is passed through several vessels or a mixed bed vessel so that both positive and negative ions are removed and water is demineralised.