Water softeners operate on the principle of ion exchange. A synthetic resin bed is charged with sodium ions by regeneration with salt (sodium chloride). Hard water, containing calcium and magnesium ions, flows through the resin. Ion exchange occurs when the calcium and magnesium ions attach themselves to the resin, displacing the sodium ions. The resultant water is softened, being free from calcium and magnesium, but the sodium content is increased.

In short, hard water enters the brine tank, becomes saturated with sodium and then enters the resin tank, where polymer beads attract the sodium molecules and the extra salt water is purged. The brine tank is refilled and unsoftened water enters the resin tank, where the calcium and magnesium trade places with the sodium and attach themselves to the polymers until there are no more sodium molecules to make the trade. At this point, the cycle starts over when the water softener regenerates by scrubbing the hard minerals off the beads and draining the wastewater.

Normally water softener systems consist of the following:

• The resin tank: This contains the cation resin
• The salt tank: This contains the salt and saturated brine solution used in regeneration.
• The filter head: This contains a timer that automatically operates the control valve that initiates the five cycles of the water softener. This clock controls the time of day that regeneration occurs and the number of days between regenerations.