How Does a Water Softener Work? + System Flow Diagram

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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 stain pipes and water-based appliances, reducing their lifespan.

This guide shares the science behind soft water, including what causes hard water and how to get rid of it.

📌 Key Takeaways:

  • A water softener is a type of water treatment system that removes hardness minerals from a water supply.
  • Traditional water softeners work by ion exchange – exchanging calcium and magnesium ions with sodium ions.
  • In order to work in the long term, a water softener must regenerate by sending salty water into the brine tank, flushing the hard minerals from the resin and replacing them with sodium ions.

🚿 What Is A Water Softener?

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

The brine tank produces salt, which is carried into the mineral tank to top up the resin bed. When water flows through the resin, hard water minerals are exchanged with sodium (salt). This is known as ion exchange.

Water softeners offer the most effective way to soften water. By removing calcium and magnesium minerals, a water softener should completely eliminate scale and other hard water issues.

⚙️ What Are the Parts of a Water Softener?

Salt-based water softeners are the most popular systems for softening water. They’re made up of three main components:

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

Mineral Tank

The mineral tank is where the water softening takes place. This tank is filled with hundreds of tiny resin beads.

When water flows through the resin, the hard water minerals (calcium and magnesium) are attracted to, and stick to, the resin. To balance the water’s charge, the resin releases equal amounts of sodium ions, producing soft water.

The softened water then exits the tank and flows into your home’s plumbing system and hot water heater.

Brine Tank

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 salt solution known as brine.

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. When the salt levels fall low, the brine tank will need to be topped up with more salt.

Control Valve

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 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.

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. 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, replacing the hardness minerals with sodium ions.

Related: The History of Water Softener Systems

Why is Salt Used In a Water Softening System?

Sodium chloride (salt) is a positively charged ion 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.

🧫 What Do Water Softeners Remove?

Water softeners are solely designed for removing hardness minerals: calcium and magnesium.

The ion exchange process also removes low levels of other dissolved minerals and metals, including iron and copper.

However, water softening systems can’t remove these minerals completely. Calcium and magnesium are the only minerals that are totally removed by a water softener.

Does A Water Softener Reduce Iron?

Yes. Water softeners the ion exchange process to remove all positively charged ions, and many systems can reduce low levels of 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.

Most water softeners can remove 3 PPM of iron or less, but some have a specialized resin that allows for slightly better iron removal.

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.

The water softening system draws a highly concentrated solution of salty water (known as brine solution) 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.

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. 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 usually 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 concentrated 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.

regeneration process

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⏱ 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.

Continue Reading: Water softener timer instructions

🚰 Water Softeners Vs Water Filters

Someone who doesn’t know much about water treatment might call a water softener “a hard water filter”. This is incorrect, since water softeners don’t actually filter water.

A water filter is designed to trap or pull contaminants out of a water supply, holding them in a filtration media until the filter becomes clogged and needs to be replaced or backwashed. Contaminants removed by water filters include chlorine, heavy metals, pesticides and herbicides, and nitrates.

A water softener addresses hard water scale, usually by removing hardness minerals from a water supply. Water softening systems don’t use filtration media and don’t remove any other common drinking water contaminants.

Whole home water filter vs water softener system

🧂 Salt-based Vs Salt-free Softeners

Salt-based water softeners, otherwise known as ion exchange softeners, are the most popular and most effective systems available today.

But there are other types of hard water treatment that are rapidly gaining popularity.

Salt-free conditioners use a salt-free process to change the molecular structure of the water, preventing 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 conditioners are a better option for people on a low-sodium diet or people who don’t want to add salt to their drinking water. However, they don’t address all hard water issues. You won’t experience better skin and hair health, and you won’t be able to use less soap and laundry detergent after installing this system type.

👉 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.

Fleck 9100SXT Dual Tank Water Softener

⚖️ Pros & Cons of Water Softeners


Most Effective Hard Water Treatment

No other water treatment tackles hard water as effectively as a water softener. Water softeners don’t just reduce scale – they eliminate it entirely.

Whole-Home Scale Prevention

A water softener is installed at water’s point of entry into a home, upstream of any water heaters, so it prevents scale in a whole home plumbing system and all the connected appliances.

Cheap To Run

The only running cost associated with water softeners is the cost of salt, which is less than $100 per year.


Add Salt To Water

Although salt-softened water is safe to drink, you might not want to add any more salt than necessary into your diet. The good news is that you can use potassium chloride instead of salt if you’re against the idea of salt softening.

Reduces Mineral Intake

Ion exchange water softeners remove hard water minerals entirely. These minerals might be damaging to a plumbing system, but they’re good for our health and give water a pleasant alkaline taste. Salt-softened water isn’t as healthy or as tasty as hard water.

Produce Salty Wastewater

When a water softener regenerates the resin beads, it sends salty water from the brine tank into a nearby drain. Not only does this increase your household water usage, but it’s also bad for the environment.

Check out our full, detailed list of the pros and cons of water softeners here.

💰 How Much Does a Water Softener Cost?

The very best high efficiency water softeners available today cost $1,200-$2,500 on average.

You can get a good water softener, without the fancy features, for as little as $800. The most expensive water softeners cost $2,600+.

We don’t recommend spending any more than $3,000 on a water softener unless it has a specific feature that you need (e.g. dual softening and filtration) or you need to upgrade to a large system for a big home.

🧪 Is Soft Water Safe To Drink?

Yes, soft water is safe to drink. The only difference between soft water and hard water is that soft water contains sodium instead of hard water minerals.

Even very hard water supplies are only treated with low amounts of sodium.

For instance, if you have 5 grains per gallon (GPG) of hard water, your water softener will only add about 37 milligrams of salt per quart of water. Compare that to a typical slice of white bread, which contains near-enough five times the amount of sodium – around 170 milligrams.

📌 The daily suggested sodium intake for a healthy adult is 2.4 grams, so drinking soft water certainly won’t push your sodium levels over the edge.

✅ How to Know If a Water Softener Works

Now you know how a water softener works – but how do you know when a water softener is working?

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 unchanged, 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
limescale before after water softener install

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

📈 How Long Do Water Softeners Last?

Water softeners usually last 15-20 years.

If you properly maintain your water softener by…

  • Ensuring the brine tank is always topped up with salt
  • Installing pre-filtration for iron, chlorine, and sediment if necessary
  • Using resin cleaners
  • Replacing worn or damaged components

… you might get longer than 20 years of use out of your softener.

Water softener resin lasts 10-20 years depending on the resin type and quality.

8% crosslink resin has a 10-year average lifespan, while 10% crosslink resin lasts about 10 years on average.

🌯 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 means far less maintenance and money spent in the long run.

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.

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.

  • Jennifer Byrd
    Water Treatment Specialist

    Jennifer is a seasoned water treatment expert with over 18 years of experience in the industry, dedicated to improving water quality for clients across the USA and around the world. Her passion for helping others and extensive networking skills have led her to hold leadership positions in organizations like the North Port Area Chamber of Commerce and the Florida Home Builders Association. Jennifer is currently a managing partner at Redbird Water of West Texas, where she specializes in providing water filtration and solutions for residential, commercial, and industrial clients.

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