The RO plant output water is passed through the cation bed and followed by the Anion bed for the demineralization. Demineralization or deionization is the process of removing dissolved salts from water by Domestic RO Plant using Ion Exchange Resin. Basically Ion exchange demineralization is a two step process with both Cation and Anion resin. The raw water called influent water is first passed through the Cation resin bed containing SAC Resin in H + form. Ca , Mg & Na are removed and the salts are converted to their respective acids .The corresponding acid containing anions like Cl , SO4 , NO3 are removed by passing the cation effluent through Anion column containing Anion resin in Hydroxyl Form. The hydrogen ion from cation neutralizes the hydroxyl ion and produces pure water. Ion exchange is an equilibrium reaction which is reversible. In the hydrogen cation Resin, Cations like Ca, Mg are exchanged for H ions.