Hard water is softened by a process called ion exchange.
The hard water flows through a bed of resin, where it attracts the calcium and magnesium out of the water. Sediment, iron, barium and radium can also be reduced. At that time, sodium flushes out the calcium and magnesium while the resin tank is in bypass. Then it will again be ready to filter the hard water minerals out. The bypass valve, although an optional accessory, is a must for every household.