The principle of ion-exchange the two consisting of a carrier of the ion exchange reaction by the skeleton and the active group. Mobile ions by ion exchange reaction can exchange group and water homosexual ion exchange, removal of calcium and magnesium ions in the water hardness to reduce the water to achieve the desired requirements. Exchange resin reaches a certain ion exchange capacity in water is saturated, then the salt solution available for resin regeneration in vivo to restore the ion exchange capacity. The ion exchange method is widely used in industrial water, boiler water, central air-conditioning water, domestic water softening treatment.