Parts of a Water Softener – Resin Tank, Brine Tank, Valve

All 10 parts on the diagram

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Start here: 5 main parts 5

Control valve The unit on top of the mineral tank that runs the softener. It sends water through the resin and starts regeneration.
Mineral tank The tall tank the water flows through to be softened. Also called the resin tank.
Resin beads Ion-exchange resin that swaps sodium for calcium and magnesium. Those make water hard.
Brine tank Holds salt and the salty water (brine) used to recharge the resin. Also called the salt tank.
Salt It dissolves in the water in the brine tank to make brine.

Other 5

Bypass valve The bypass valve, where the house’s water pipes connect. Turned to bypass, water goes round the softener, for repairs.
Drain line It carries the waste water from regeneration away to a drain.
Brine line A tube carrying brine from the brine tank to the control valve. It does this during regeneration, and carries water back to refill the tank.
Overflow A fitting and line on the side of the brine tank. They carry water to a drain if the tank ever overfills.
Float It sits in the brine well. It shuts off the water when the brine tank has refilled to the right level.

How this list was compiled: Read 2026-09-28. (1) Wikipedia, Water softening, https://en.wikipedia.org/wiki/Water_softening : hardness is calcium and magnesium; ion-exchange resin releases sodium ions and captures calcium; recharging (regeneration) backwashes the resin to a drain, draws brine through it, rinses, and refills the brine reservoir; the waste water goes to the sewer. (2) Maker’s installation manuals on archive.org (https://archive.org/details/manualzilla-id-6860835 and https://archive.org/details/manualzilla-id-6860502): control valve, bypass valve, mineral tank, resin, brine tank (salt tank), brine line, float, drain line, overflow. Licence: own work

The drawing: Drawn for this site by script, 2026-09-28. Own work, nothing traced. Licence: own work

How it works

These are the parts of a water softener on a two-tank ion-exchange softener, both tanks cut open to show the resin and the salt. Start with the 5 main parts.

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Softening the water

Hard water enters through the bypass valve and control valve and flows down through the resin beads in the mineral tank. The resin traps the calcium and magnesium that make water hard, giving off sodium in exchange.

Recharging the resin

Now and then the control valve starts a regeneration. It backwashes the resin, draws salty brine from the brine tank along the brine line, rinses, and sends the waste down the drain line. The float stops the brine tank refilling too far.

Keep the salt above the water line in the brine tank; with no brine to recharge the resin, the water turns hard again.

Questions and answers

What are the two tanks on a water softener?

The tall mineral tank holds the resin beads that soften the water. The shorter brine tank holds salt and water, making the brine that recharges the resin.

What does the resin in a water softener do?

It captures calcium and magnesium from hard water and releases sodium instead. When it is full, brine washes the hardness off so it can work again.

What is the bypass valve for?

Turned to bypass, it sends water round the softener instead of through it, so the softener can be serviced without shutting off the house's water.