ION EXCHANGE RESINS are synthetic organic compounds capable of ion exchange reaction. They are widely used in the drinking and industrial water purification. The ion exchange resin is reacted with aqueous ions solution, altering its composition. It changes divalent ions (calcium and magnesium) for sodium, when passing the hard water through an ion exchange resin. Depending on the absorption particles properties can distinguish two main ion exchange resins classes – cation exchange resin (cation) and an anion exchange resin (anion). Most common in the industry are ion-exchange resins based on a copolymer made of divinylbenzene, styrene and polyacrylates, which accounts for 85 % of production.