The raw water passes successively through two columns namely Cation And Anion Exchangers. The Cation Exchange column contains strongly acidic resin in Hydrogen form. All the dissolved solids causing hardness such as Calcium, Magnesium etc. are exchanged with H* and get converted into corresponding acids. The acidic effluent is then passed through the Anion Exchange column wherein the Anion resin in hydroxyl (OH)-form retains the bicarbonate, chloride and sulphate ions, producing water equivalent to distilled water.

After predetermined quantity of water passes through the Demineraliser, all the resins contained in both columns get exhausted and require regeneration. The cation is regenerated with Hydrochloric Acid and Anion resin with Sodium Hydroxide (Caustic Soda).