Answer:

Water is demineralized by passing it through anion and cation exchange resin. It has many of SO3H and COOH groups. A cation exchanger removes cations like Na+ and Mg+ from the water. OH-, NO3-, and other anions are removed by exchanging with OH- ions in the anionic exchanger. Finally, the H+ and OH- generated mix to form water. Ion exchange resin demineralizes water.