How Does a Water Softener Work? (2024)

Updated on:
January 26, 2024

If you’ve stumbled across this article, you’re either at a point in your life where you’re investing in home improvement or you’re thinking about going into plumbing. Or neither.

Maybe you make it a habit to understand the underlying mechanism of every household appliance. Maybe you’re thinking about installing your water softener. After all, learning how it works will help you ensure it is working after you install it.

Whatever your motivation, you’re in the right place.

As you probably know already, a water softener is responsible for turning hard water into soft water. If you’d like a primer on what a water softener is, I have an article on that, too.

But how does it work? Chemistry. To truly understand how a water softener works, you’ll need to think about all that sciencey jargon you’ve repressed from high school, like ions and charges. And if you happen to love chemistry, you’ll feel right at home.

For now, sit back, relax, and enjoy learning about how a water softener is able to, you know, soften water.

What is “hard” water?

As a homeowner or renter, you’ve probably heard of water hardness by now. And maybe you’ve thought, “Huh, what a weird way to describe a liquid.” Or maybe that’s just me.

Anyway, water hardness refers to the mineral content within the water, including whatever calcium, magnesium, and other metals are dissolved and floating around. 

The metric for water hardness is milligrams per liter (mg/L). The U.S. Geological Survey defines the ranges for water hardness:

  • Soft: 0-60 mg/L
  • Moderately hard: 61-120 mg/L
  • Hard: 121-180 mg/L
  • Very hard: 180+ mg/L

You can test water hardness yourself by purchasing a kit from your local hardware store. Or you can have a water softener company come in and do it for you. Many of these companies offer free tests, so it’s worth a shot.

Now, for all you well water people out there, here’s some bad news—you probably have more calcium and magnesium ions than the average household. That’s because minerals in the surrounding soil are more likely to dissolve into your water supply. 

Salt-based water softener

Now that we’re all on the same page with water hardness, it’s time to get into the most common type of water softening system—the salt-based water softener. This is also known as an ion exchange system. You’ll see why shortly.

Mineral Tank

In the anatomy of the salt-based water softener, the mineral tank is the heart. It’s the part that actually creates the softened water using chemistry, which you can’t avoid when it comes to treated water.

First up, you should know what’s inside the mineral tank— the negatively charged resin beads. If you remember any part of chemistry, it’s probably that opposites attract. You know, like magnets. So the resin beads are actually holding onto sodium ions before hard water enters the scene.

Those positively charged sodium ions balance the negative charge of the resin beads—until the hard water flows through. Once incoming water from the main line flows through the mineral tank, all those hard water minerals start interacting with the resin beads. 

A lot of smart people have worked on perfecting this system over many years, so those resin beads are designed specifically to handle this kind of interaction. They are porous in structure, with chemical sites that have specific chemical interactions with positively charged sodium ions. That is, the resin is designed to let sodium ions come and go.

When positively charged calcium and magnesium ions come along, they displace those sodium ions and attach themselves to the resin beads. At this point, you might be wondering, “Hey, why did the sodium ions get kicked out if they are also positively charged?”

That’s a valid concern. After all, sodium was there first, claiming its spot on the resin before any mineral ions were in the picture. As it turns out, the charges on calcium and magnesium ions are stronger than the charges on sodium. 

So sure, all of these ions have positive charges, but magnesium and calcium have a stronger attraction to the resin beads. And that’s where the whole “ion exchange” label comes in. As hard water moves through the mineral tank, the sodium ions are being swapped for hardness minerals.

Brine Tank

So does the mineral tank do all the work? Nope.

While the resin is working to exchange those ions and remove minerals from the water supply, the brine tank handles another essential part of the water softening process—the regeneration cycle.

The brine tank is about half full of sodium chloride (or, as most people call it at the dinner table, salt). To understand the significance of sodium chloride in the regeneration process, you’ll need to think back to the ion exchange stage. That shouldn’t be too hard since we discussed it about three paragraphs ago.

By now, we know that hard water became softened water through resin beads picking up hardness minerals (like magnesium and calcium) and dropping off sodium into the softened water. But what happens when all those resin beads are filled up with calcium and magnesium?

When that’s the case, the resin beads have reached maximum capacity and can’t attract any more mineral ions. That means hard water will stay hard and release into your plumbing system and household water. Eventually, those hard water deposits can build up in hot water heaters, make your washing appliances run less efficiently, and affect your hair and skin.

It’s time to recharge the mineral tank through the regeneration process. To initiate this process, water is added to the brine pellets to create a salt solution. The salty water then enters the mineral tank to displace the calcium and magnesium ions in the resin.

As we established before, when the hard water passes through the resin tank, the resin is responsible for removing hardness minerals by swapping sodium for hard water ions. 

The brine tank holds a highly concentrated solution of salt to sweep through the mineral tank during the regeneration cycle. Those high concentrations of salt solution wash through the resin beads and overwhelm the calcium and magnesium ions to the point that those mineral ions get displaced by sodium. 

Thus, the regeneration process uses ion exchange to reset the resin, allowing it to continue to create soft water. All those hardness minerals get washed away from the resin, leaving room for more calcium and magnesium to get taken up from the hard water.

After the regeneration process is over, the water softener system is ready to resume normal operation.

With all this ion exchange talk, you might be worried about the sodium in your drinking water or the water you use to wash your food. If you’re on a low-sodium diet or just don’t want higher levels of sodium in your water, a possible solution is using potassium chloride instead of salt in the brine tank.

But beware—potassium chloride typically costs three to four times more than sodium chloride. Depending on how much water your household uses, you could be replacing salt pellets used in the regeneration process every couple of weeks. Those costs add up.

There is yet another option when it comes to your brine tank and brine solution. If you want to keep costs down with sodium chloride pellets but don’t want sodium in your water supply, you can also install a reverse osmosis water filter at the kitchen sink. Salt-based water softeners can be used for the entire house, and then the reverse osmosis water filter will take out any sodium and other contaminants before you drink that water.

Salt-free water softener

Aside from conventional water softeners, there are high-efficiency water softeners that don’t require ANY salt.

Since I just went through all the nitty-gritty details of the brine tank, brine solution, and regeneration process of salt-based water softeners, this concept might be a little confusing.

It becomes even more confusing when you realize that salt-free water softeners aren’t technically considered water softeners. They’re “water conditioners.” What’s the difference?

Instead of using ion exchange to create softened water, salt-free water softeners chemically alter calcium and magnesium ions so that they can’t get stuck to surfaces or build up in your pipes and water heater.

This is accomplished through template-assisted crystallization, which conditions calcium and magnesium by chemically altering their form. That means that a salt-free water softener will keep minerals from restricting water flow in a home, but technically the minerals are still in the water supply.

If you’re particularly worried about sodium in your water supply through a traditional salt-based water softener, salt-free might be the way to go. Plus, there won’t be any brine solution to maintain because a brine tank is unnecessary. Instead, there’s one tank with potassium.

Reverse osmosis water softener

Like a conventional salt-based water softener, the reverse osmosis water system is great at removing minerals that would otherwise restrict water flow into your home. But how it operates is just a tad different.

Whereas ion exchangers use the dual-mineral tank and brine-tank system, a reverse osmosis system uses a sediment filter, a carbon filter, and a semipermeable membrane (as explained by Fresh Water Systems).

The sediment filter does what it sounds like it does—removes sediment. That includes any dust and other muck floating around. The carbon filter takes out contaminants. Finally, the semipermeable membrane takes out dissolved solids by allowing water molecules to pass through without letting those contaminants through with them.

This revolves around another concept from chemistry—osmosis. A reverse osmosis water softener uses the principle that a solution will try to reach equilibrium by flowing from low concentration to high concentration. A reverse osmosis system applies pressure to the side of the membrane with a higher concentration, forcing that solution through. That also forces dissolved solids and contaminants to get left behind.

There are some disadvantages to this system. For example, it softens and purifies water slowly compared to other types of water softeners. Also, you’ll have to replace that membrane fairly often as it traps bacteria.

One popular solution is installing a small reverse osmosis system in the kitchen so it supplies your kitchen faucets. That means using it in combination with another kind of water softener. After all, it’s really good at generating drinking water. It just does it at a snail’s pace.

Magnetic water softener

Magnetic water softeners are the most controversial of the systems discussed so far, partially because they’re relatively new and partially because their efficiency is debatable.

These are also known as electronic water systems, if you’re curious. According to generic water softener companies, these systems involve attaching powerful magnets to your pipes that alter magnesium and calcium ions as they pass by. That alteration prevents these minerals from building up in your pipes, water heaters, and surfaces.

Can the magnets reach all of the minerals in your hard water as it passes through the system? The results are debatable. Most water softener companies and users agree that a magnetic water softener is a step down from more conventional options, though it is better for the environment.


If you’ve ever Googled, “How does a water softener work?” you know there are a million different results. Many have confusing words and diagrams that are, unfortunately, necessary to fully understand the intricacies of a water softener.

BUT you have this article under your belt, now. You know what hard water is along with how it becomes softened water, at least at a basic level. You’re practically a chemist.

You also might be on your way to becoming a water softener connoisseur. But wouldn’t it be nice if someone else could do all the water softener research and put it all in a nicely formatted article for you to read? 

Don’t worry, I’ve got you covered. And if you’re looking for the

In the meantime, you can revel in all your newfound knowledge about softened water. Remember, someone asking you, “How does a water softener work?” isn’t an if—it’s a when. Now you have the answer. 

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