What is a Water Softener? How Does a Water Softener Work?

Author: Rory Mullan - Published: 2021/07/16 - Updated: 2022/11/08

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As more people are learning about the impact of hard water on appliances and plumbing, the hype of water softeners is increasing. But what exactly is a water softener, and what does water ‘softening’ refer to?

Before you buy a water softener, it’s best to understand how it works. Don’t worry; you don’t have to read a complicated user manual. Instead, go through this article to learn the basics.

So, here is our guide on traditional salt-based water softeners and how they work!


  • Water softeners are called such because they remove hardness-causing minerals (calcium and magnesium) from hard water making it soft.
  • Hard water enters the water softener system through its head valve. The head valve controls the flow and direction of water.
  • In softening mode, water is directed into the resin tank containing resin beads that bind all hard water minerals.
  • To regenerate the resin beads, they are backwashed with a highly concentrated solution of saltwater called “brine”. Salt and brine are stored in the brine tank.

What is a Water Softener?

A water softener is a piece of equipment that removes hard minerals, such as magnesium and calcium, from water. All water softeners serve the same purpose: they soften water.

How they do so might differ just a little bit from one model to another.

The final goal of a water softening system is to minimize scale buildup on your appliances, faucets and overall plumbing to ensure your maintenance and repair costs are low.

The 3 Essential Components of a Water Softener

Here are the three main components of a salt-based water softening unit:

  1. Resin tank: The resin tank houses the main softening force. The ‘resin bed’ is lined with salt ions and traps the hard minerals while letting the salt dissolve in your water.
  2. Head valve: The control or head valve is above the resin tank. Its primary function is to control the water softener. You can change the settings on the head valve to control water flow and direction.
  3. Brine tank: The brine tank contains up to a few hundred or more pounds of salt. It is where brine is mixed for regeneration.

Some systems may have additional components while others may be more compact. For instance, the brine tank and resin tank are combined in cabinet-style water softeners. Thus, these models are better for homes with limited space.

Other Components

Apart from these 3 main parts, here are the other components that most water softening systems feature:

  • Flow meter: It measures how much water passes through the unit.
  • Bypass: Some models contain a built-in bypass so that you can turn the system off for maintenance and repairs. The bypass is also on during system regeneration. This causes unsoftened water to flow through the supply line.
  • Resin bed: A resin bed consists of tiny beads made of a natural or synthetic material. It’s a polystyrene compound in most cases.
  • Valve motor: The motor causes the rotation of the rotor valve to perform different functions, such as regeneration and softening.
  • Salt: It forms a brine solution after mixing with water.
  • Distribution tube: The distribution tube is inside the resin tank and allows water to go from the tank to the head valve. Plus, there’s a basket under the tube that keeps the resin from leaking into your water supply lines and plumbing.
  • Grid plate: The plate is in the brine tank and specifies the amount of salt and the volume of water.
  • Brine float: The safety float prevents overfilling of the brine tank by shutting off the water supply when the water goes above a certain level.
  • Brine injector and tube: The brine injector brings brine through the brine tube to the resin tank using negative pressure.
  • Pre-filter: Although it’s optional, a pre-filter is a valuable component of any water softener since it removes large particles, such as silt and sand, from water before it reaches the resin tank.

How Does a Water Softener Work?

How Does a Water Softener Work Thumbnail

Now that you know about all the different parts of a water softener, you need to understand how they function together.

So, how do water softeners work?

The problem begins when hard water comes to your house. It’s considered ‘hard’ because it contains certain minerals, mainly magnesium and calcium. In some cases, manganese and iron may also contribute to water hardness.

Once hard water enters your main water supply line, it goes through the following softening steps in a water softener:

  • Initially, the water enters the head or control valve of the softener.
  • Then, it flows into the resin tank, where softening takes place.
  • At the resin, the water passes to the distribution tube and meanwhile comes in contact with the resin beads layered with sodium ions. In some cases, potassium chloride is used as replacement for sodium. Potassium is easier to treat for the sewage department and is more eco-friendly than sodium. However, it’s more expensive.
  • An ion exchange process takes place here. Calcium and magnesium ions attach themselves to the resin beads replacing the sodium ions which go into solution. Ideally, the water is free from hard water minerals before it enters the distribution tube to exit the resin tank.

What Does a Water Softener Do? Ion Exchange!

Ion exchange is a sort of swap that takes place between charged atoms. The hardness minerals have positive charges on them, while the resin media is charged negatively.[1]

Thus, the opposing forces attract each other like magnets. Since magnesium and calcium have stronger charges, they replace the sodium from the resin.

In the end, the soft water contains sodium while any calcium/magnesium stays stuck to the resin.

What is Regeneration?

If you’ve ever done your research about water softeners, you must have come across the term ‘regeneration’ or regenerating cycle. Here’s what it means.

As the resin media removes hard minerals from water, a point will come when there will no longer be any sodium ions for the calcium and magnesium to replace. That’s when the system requires regeneration to flush out all accumulated hard water minerals and restore the resin with new sodium ions.

What’s the fate of the calcium and magnesium ions that the resin media trapped earlier?

They all go down the drain. Meanwhile, the brine tank flushes the resin with a high concentrated salt solution and recharges it.

The whole process takes place in steps, as discussed below:

Step 1: Backwashing

During regeneration, the softening unit first goes into bypass so that the main water supply gets unsoftened water. That’s why regeneration cycles are run during low-consumption times of the day.

In backwashing, the water flow is reversed. Water goes through the resin tank from the bottom upwards, through it, and out. The step is important for expanding the resin.

As a result, any debris or sediments in the system go down the drain.[2]

Step 2: Brining

After backwashing, the direction of water flow goes back to normal. As fresh water flows down the resin tank, it creates a suction effect, bringing salt-saturated water from the brine tank to the resin tank via the brine tube. As the brine flushes through the resin media, it covers the beads with fresh sodium ions.

Now, you might be thinking, if sodium has a weaker charge, how does it replace the hard minerals on the resin media? It has a lot to do with the concentration of sodium in the brine solution.

Sodium’s concentration in the solution is so high that when it washes over the resin media it releases all hard minerals from it. As brine passes through the resin tank, the hard minerals keep washing out until almost none of them remain.

water softener brine tank with salt

Step 3: Rinsing

In this stage, the unit removes any remaining brine and mineral content.

First the rinsing is slow. Another subsequent rinse – but faster – flushes everything that’s left down to the drain. Also, the flow force is so high that it compresses the resin media into its original state.

Step 4: Refilling

Since all the brine from the brine tank has been used to recharge the resin, the tank is refilled for following regeneration cycles.

A regeneration cycle takes about an hour or two to reach completion. Once the softening unit has regenerated, the bypass is lifted, and the flow of soft water to the supply line is restored.

Regeneration is extremely important since it allows a water softener to work smoothly for years. Plus, if you do not run regeneration cycles, your softener will be of no use since there will no longer be any ion exchange capacity left.

How Do Commercial Water Softening Systems Work?

Commercial water softening systems are just like residential ones. They also have a sodium-charged resin media that removes magnesium and calcium from the water. Thus, they work according to the ion exchange mechanism that you see in standard water softeners.

Naturally, these softeners are often much larger and serve bigger spaces.


In conclusion, a water softener removes hard water minerals producing soft water. The overarching goal is to minimize limescale damaging the plumbing system in a house.

Every water softener requires three main components: a resin tank, a brine tank and a control valve.

The process behind salt-based water softening is called ion exchange. It replaces hardness minerals in water with salt.

When a water softener has depleted its softening capacity, it goes into regeneration. During the cycle, the resin bed is backwashed at first. Then it’s recharged during the brining phase. This is followed by a slow and a fast rinse to clean and pack the bed. Lastly, the brine tank is refilled.

Further Reading


Meet Rory Mullan

Rory Mullan Rory has joined the Water Masterz team as a contributing writer. He has covered all sorts of topics in the last several years.

Outside of his writing work, Rory enjoys photographing the Irish landscape and making music!

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