How Does a Water Softener Work? + System Flow Diagram

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

Hard water contains calcium and magnesium minerals, which are responsible for limescale – known to cause all kinds of issues around the home.

Hard water scale clogs plumbing and lines the surfaces of water-based appliances, reducing their lifespan.

If you’re considering buying a water softener for your home, you’re probably keen to learn the exact process you can expect from a standard salt-based softener.

This guide will share the science behind soft water, including what causes hard water and how to get rid of it. By the end, you’ll have the knowledge to make the right purchase based on your water softening needs.

⚙️ What Are the Parts of a Water Softener?

Salt-based water softeners are the most popular systems for softening water, using the ion exchange process to swap calcium and mahynesium minerals for sodium ions. They’re made up of three main components:

  • A mineral tank (otherwise known as a resin tank)
  • A brine tank
  • A control valve

The mineral tank is where the water softening takes place. This tank is filled with tiny resin beads. When water flows through the resin, the hard water minerals (calcium and magnesium) are replaced with sodium ions. The softened water then exits the tank and flows into your home’s plumbing system, through your water heater, appliances, and fixtures.

The brine tank holds the sodium, or salt, ready for use. The salt mixes with the water at the bottom of the tank to form a brine solution. When the water softener regenerates, it draws the brine solution from the brine tank into the resin tank. The brine solution washes through the resin beads, replenishing them with sodium. This process repeats itself every time the water softener system regenerates. It’s important to top up the brine tank with salt when the salt levels fall low.

The control valve controls how much water flows out of the resin tank and into your home. The valve is metered, enabling it to track the volume of water entering and flowing through the mineral tank. In a demand-initiated water softener, the control valve will schedule the softener to perform a regeneration cycle once a certain volume of water has passed into the resin tank, ensuring that the resin beads are replenished with sodium ions on time.

Related Review: The Most Efficient Upflow Water Softener Systems

How a water softener works

🤔 So, How Does a Water Softener Work?

The softening process begins when water enters the system from the main water supply line.

Water flows into the mineral or resin tank, containing a bed of resin. The resin beads in the tank are negatively charged, and attract positively charged sodium ions.

The calcium and magnesium mineral ions in the water are positively charged. The opposite charge of the resin attracts the calcium and magnesium ions and traps them.

When this happens, the resin beads release equal amounts of sodium ions to balance out water’s charge, replacing the hardness minerals with sodium ions.

Why is Salt Used In a Water Softening System?

Sodium chloride (salt) is a positively charged mineral that doesn’t have aesthetic or health effects in low levels in drinking water, making it a good choice for use in a softened water system.

Most water softeners use salt because it’s affordable, efficient, and easy to find.

If you prefer not to contribute to your sodium intake or you follow a low-sodium diet, you can use potassium chloride as an alternative to salt in your softening system.

Potassium chloride is more expensive and less efficient than salt, but it works just as effectively to produce softened water as long as you adjust your settings to accommodate this ion.

Does the Average Water Softener Reduce Iron?

Yes. Water softeners are capable of attracting and holding onto positively charged ions, and many systems can reduce ferrous (clear water) iron in water, which is also found in ionic form.

Iron is known to cause staining on plumbing appliances, and can affect water taste and flavor in some forms.

A water softener uses the ion exchange process to exchange iron ions with sodium ions – exactly how it exchanges calcium and magnesium with sodium.

water softening process

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➰ 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. This is where the brine tank comes in use.

The water softening system draws a highly concentrated solution of salty water (known as brine) out of the brine tank and flushes the resin bed to wash away the calcium and magnesium minerals, replenishing the resin with sodium. This recharges the resin, preparing it for water softening once more.

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.

Once the discharge water is removed from the system, it’s flushed down a drain, which is connected to your home’s sewer or wastewater system.

Finally, the system rinses itself out with water, before the softening process begins again.

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

Co-Current Regeneration

The co-current regeneration process sends the brine solution into the resin tank in the same direction as the water flow. The brine washes down through the resin beads, and a reverse of the ion exchange process takes place.

The force of the brine flowing over the beads causes the magnesium and calcium hardness ions to be released, and sodium takes their place.

As the brine flows through the resin beads, the hardness minerals are forced down through the system, causing them to constantly be exchanged and re-exchanged. As a result, 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.

A co-current regeneration cycle is less efficient than a counter-current cycle, using more salt and more water.

Counter-Current Regeneration

The counter-current regeneration process sends water up through the bottom of the regeneration tank, where water typically leaves the 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 strong once it reaches the top of the tank.

A water softener using a 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. Counter-current softeners are also known as high-efficiency water softeners.

regeneration process

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💭 Additional Considerations

There are several other factors to consider when it comes to how a water softener works. Here’s what else you may need to know:

Metered Vs Timed Water Softener

A metered water softener regenerates based on the volume of water that flows through the system (calculated by the control valve).

A timed water softener regenerates after a certain amount of time has passed (calculated by the system’s built-in timer).

Metered water softeners offer the most efficient way to produce softened water. These systems only regenerate when they need to, while time-based regeneration often causes a system to regenerate when there is still sodium left in the resin tank.

Salt-based vs Salt-free Systems

In this guide, I’ve focused solely on salt-based water softeners, otherwise known as ion exchange softeners, as these are the most popular (and some would say most effective) available today.

But there are other types of filtration that are rapidly gaining popularity, especially salt-free water conditioners.

This type of system, as the name suggests, uses a salt-free process to change the molecular structure of the water. For this reason, it’s advertised as a better option for people on a low-sodium diet, or people who just won’t want to add salt to their drinking water.

Instead, they use a chemical process to transform the calcium and magnesium, giving them a different structure that prevents them from being able to bind to surfaces in the form of limescale. These units do not perform well on extremely hard water.

Salt-free systems aren’t technically considered water softeners; rather, water conditioners, as they don’t actually remove the hard water causing the calcium and magnesium ions from water.

👉 Check out our reviews of the best ion exchange water softening systems

Single vs Dual Tank

The majority of water softeners are single tank units. However, dual tank, or twin tank systems are growing in popularity, because the system has two tanks, making the entire softening process more efficient.

This is because one tank can regenerate while the other takes over with water softening. If you’re looking for a water softener that’ll work 24 hours a day, a dual tank softener is for you.

It’s best to get a dual tank water softener that will regenerate as and when needed than to get a single tank softener that regenerates on a timer.

Using a timer-based regeneration instead of letting the system regenerate when it needs to means your water softener won’t be anywhere near as efficient as it could be, as it’ll be regenerating needlessly, even when there are still free resin beads in the mineral tank.

✅ How to Know If a Water Softener Works

Now you know how a water softener works – but what’s the proof that your system provides ion exchange effective softening?

For a water softener to effectively work, it needs to turn hard water into soft water.

You can evaluate the effectiveness of a water softener by testing your water upstream and downstream of your water softener.

The water upstream of your softener – i.e. the water that hasn’t yet been softened – should have your usual hard water reading.

The water downstream of your softener – i.e. the soft water that has left the mineral tank – should have a hardness reading of less than 3 GPG (grains per gallon).

You can use an at-home test kit to measure the hardness minerals in your soft water. If your water hardness is unexpectedly high, you may have an issue with your softened water system.

Aside from softened water with a reduced mineral content, other signs that your softener is working are:

  • Smooth, silky water
  • Reduced problems with dry skin or dull hair
  • No limescale or mineral spitting in your household water system
  • System regenerates according to the anticipated timetable
  • Salt top-ups are regular and as expected

On the other end, signs that your softener isn’t working are:

  • Hard water leaving the mineral tank
  • Unusual noises coming from the system
  • The system stuck in a constant regeneration cycle
  • A change to your water quality, including appearance, taste, and odor
  • Sticky or slightly dry skin after washing
  • Hard water deposits and mineral spotting on your water-using appliances

🌯 Wrap Up

Many people ask whether water softeners are really necessary.

The answer: it depends.

If you currently have moderately hard to very hard water and you’re looking to…

  • Extend the lifespans of your water-based appliances
  • Cut down on hours of cleaning
  • Improve your water’s ability to lather
  • Prevent staining on your glass fixtures and dishware

… then you’ll appreciate the benefits a water softener can bring to your home.

Having a scale-free water supply will mean far less maintenance and money spent in the long run, which is an attractive prospect to anyone who plans to live in their home for the foreseeable future.

Water softeners work very effectively for their price, and you can usually get a great deal on a system that will last you for years and years with minimal maintenance. You can spend less than $1,800 on highly effective a hard water solution for the next decade or so.

For the majority of people who invest in a water softener for their home, the money spent is more than worth it for the softened water benefits they can enjoy.