How Does a Water Softener Work?

The three parts of a softener

A typical salt softener has three pieces:

• The resin tank (also called the mineral tank). The tall tank full of resin beads, which Kinetico describes as millions of small beads designed to attract hardness minerals.
• The brine tank. The shorter tank you pour salt into. Water sits in the bottom and dissolves the salt into brine.
• The control valve. The head on top of the resin tank. It routes water through the resin in service and runs the regeneration steps on a schedule or when the meter says capacity is used up.

Ion exchange: what happens in service

The resin starts out coated with sodium ions. As hard water passes through, the resin trades its sodium for the calcium and magnesium in the water. The hardness minerals stay stuck to the beads, and the water leaves with a little sodium instead.

How much sodium? Penn State Extension puts it at about 7.5 mg per quart for each grain per gallon of hardness removed. Penn State flags that added sodium as a potential health risk for people on low-sodium diets. Some softeners can run on potassium chloride instead of salt, and Kinetico notes the resin beads can carry either sodium or potassium ions.

Regeneration: how the beads get recharged

Eventually the resin runs out of sodium to trade. Then the control valve runs a regeneration. On a Fleck 5600SXT, a common valve, the steps are:

1. Backwash (BW). Water flows up through the resin to loosen it and wash out grit.
2. Brine draw and slow rinse (BD). The valve pulls brine from the brine tank through the resin, and the sodium knocks the calcium and magnesium off the beads. The minerals go to the drain.
3. Rapid rinse (RR). Fresh water flushes out the leftover brine.
4. Brine tank fill (BF). The valve sends fresh water back to the brine tank so the next batch of brine can form.

Then the valve returns to service. Penn State says one regeneration uses about 50 gallons of water. That's why softeners need a drain nearby, and why the regeneration time belongs in the middle of the night.

How the brine tank works

The brine tank is the simple part. After each regeneration the valve refills it with a measured amount of water. That water sits in contact with the salt and dissolves it into a strong brine. Pentair's manual says the refill water has to come above the grid plate and touch the salt. If the salt forms a hard crust above the water, called a salt bridge, no brine forms and the softener stops softening even though the tank looks full. See salt bridge for how to break one.

Timer, metered and twin-tank softeners

How the softener decides when to regenerate matters more than most buyers realize:

• Timer (time clock). Regenerates every few days on a schedule whether you used the water or not. Penn State notes this can waste water and salt.
• Demand control (metered). Counts gallons and regenerates after a set amount of water has been softened. This is the one to buy.
• Twin tank. One resin tank works while the other regenerates. Kinetico's twin-tank units supply soft water around the clock without a timer.

Our regeneration settings guide covers how often yours should run.

How a salt-free "softener" works

A salt-free conditioner works differently. It doesn't remove hardness. Kinetico says these systems crystallize the hardness minerals so they're less likely to form scale, but the minerals stay in the water. Many use a sequestering agent that links hardness ions together. They need no salt and no drain, which is the appeal. They don't give you the slick soft-water feel or stop spots the way a salt softener does. Compare them on our salt-free vs traditional softener page.

How to tell if your softener is working

• The salt level drops over a few weeks. If it never moves, the unit isn't drawing brine.
• Soap lathers easily and the shower feels slick.
• A hardness test strip at a kitchen tap reads near zero.
• You can hear it run in the night at the regen time.

If the water still feels hard, start with our water softener not working checklist.