Removal of hardness from water is called softening. The softening is done by ion exchange process. The ion exchange process works on the replacement of the calcium and magnesium ions in the water by an This eliminates the unwanted charasteristic of hard water because the sodium salt neither form scale nor a scum with soap but only lather.The resin will take up the calcium ion to the extent of what sodium ions resin will have with it. equivalent number of sodium ions.