Most softeners use the principle of ion exchange. This is a process whereby undesirable mineral ions are removed from water and replaced by desirable ones that were stored on the ion exchange medium. When the exchange medium becomes saturated with undesirable ions, the unit is removed from service and recharged by passing a concentrated solution of the desirable ions over the medium. This reverses the ion exchange process and causes the undesirable ions to be replaced by the desirable ones.

Reprinted with Permission from Chem-Aqua