Water softeners operate by a mechanism called ion exchange that eliminates water from calcium and magnesium. It flows through a bed of spherical resin beads as the hard water reaches the mineral tank.

These plastic beads are charged with a sodium ion, usually made from polystyrene. The resin beads are anions, which means there is a negative charge on them. There is a positive charge in the calcium and magnesium minerals, making them cations.The negative charge of the minerals is drawn to the positive charge of the resin beads due to the attraction of opposite charges.

The beads take hold of the mineral ions and expel them from the water as the hard water moves through the resin. The sodium ion is then released as the bead seizes the mineral ion. When it moves through the mineral tank, the resin column takes all the toughness out of the water, and softened water flows out into your house.