All salt based water softeners use the process of ion exchange to create soft water. Inside a water softener is a vessel of resin beads. Hard water passes over the resin beads which extract the hard minerals (calcium and magnesium) and replace them with harmless sodium ions. Scale is therefore taken out of the water which leaves the water softened.
The resin beads will eventually become exhausted and unable to pick up any more hard minerals. The softener will carry out a regeneration or recharge which will flush the hard minerals to drain. The recharge or regeneration process passes a salt water solution through the resin beads which detaches the hardness minerals, which are flushed harmlessly to the drain. The resin beads are left refreshed and ready to make more softened water.