How Do Water Softeners Work? + System Flow Diagram (2025)

Water softeners address one of the biggest water quality problems: hard water.

We’ve been researching and reviewing the best water softeners for more than 10 years. In this guide to how water softeners work, our experts are on hand to share the science behind soft water.

🚿 Water Softener Main Components

• Resin tank – The main softening tank, where the ion exchange process takes place. It contains a bed of resin beads, which are loaded with sodium ions.
• Brine tank – Contains the salt to supply the resin beads with sodium. Salt mixes with water in the tank to form a brine solution.
• Drain line – Where the brine solution is flushed out of the water softener during a regeneration cycle.

🤔 How Does a Water Softener Work?

A water softener is a water treatment system consisting of two tanks: a resin tank and a brine tank.

Water softeners work by using a process called ion exchange – specifically, a type of ion exchange known as cation exchange.

Here are the steps involved in this process:

1. Hard water enters the water softener’s resin tank, which contains a bed of negatively charged resin beads.
2. Calcium and magnesium hardness ions in the water, which have a positive charge, are attracted to the negative charge of the resin bed. As water flows through the resin tank, these mineral ions stick to the resin beads.
3. Positively charged sodium chloride ions, which are loaded in the resin beads, are released into the water. Sodium is released, equal to the amount of hardness minerals captured, balancing the water’s charge.
4. The water, now softened with sodium ions, leaves the water softener resin tank.

Why is salt used in a water softener? Sodium chloride (salt) is a positively charged ion that readily replaces calcium and magnesium in the ion exchange process, making it a good choice for use in a water softener. Most water softeners use salt because it’s affordable, effective, efficient, and easy to come by.

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➰ The Water Softener Regeneration Process

When the resin beads in the mineral tank become saturated with calcium and magnesium ions and the sodium depletes, the water softener will regenerate.

Why do water softeners need to regenerate? Because without regenerating, the resin bed would eventually be:

• Packed to the brim with calcium and magnesium ions
• Depleted of sodium ions

Water softeners must regenerate to replenish the sodium ions and flush away the accumulated water hardness minerals.

To regenerate, a water softener draws a highly concentrated solution of salty water (known as brine solution) out of the brine tank and flushes it through the resin beads. The process usually takes 2-3 hours in total.

Here’s the step-by-step process of a water softener regeneration cycle:

1. Salt in the brine tank is dissolved in water, creating a salt solution called brine.
2. This brine solution is carried into the resin tank, where it rinses the resin beads and replenishes them with sodium.
3. The brine solution (now called the discharge solution), which contains hard water minerals from the resin, is flushed out of the water softener’s drain line.
4. The system rinses itself with water.
5. The resin is now recharged, ready for water softening once more.

A word on salt top-ups: the brine tank should be at least one-third full of salt so that the brine solution can clean and flush the hard water minerals that have built up during ion exchange. Most people top up the salt levels in their water softener brine tank every 3-6 weeks.

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There are two common regeneration methods used in ion exchange water softeners: co-current and counter-current regeneration.

• Co-current regeneration sends the brine solution into the resin tank in the same direction as the water flow. As the brine solution flows through the resin beads, the hardness minerals are forced down through the system, causing them to constantly be exchanged and re-exchanged. Once the water reaches the bottom of the resin tank, the solution is weakened, and the resin beads with the highest charge are at the top of the tank.
• Counter-current regeneration sends brine up through the bottom of the regeneration tank. The brine solution flows in the opposite direction, first coming into contact with the bottom of the resin, which is typically less depleted than the top. There are fewer hardness minerals causing exchange and re-exchange as the brine flows through the resin, which means the brine is still relatively concentrated once it reaches the top of the tank. Counter-current regeneration distributes sodium ions more evenly around the resin, which saves about 65% water and 75% salt compared to a co-current water softener.