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How Does a Water Softener Work?

Thinking about taking the plunge and getting a home water softener? We explain how these devices work and why sometimes they’re necessary. We also list a few features that you should be looking out for.

hard water deposits

Water hardness can mean the difference between a smooth-running household whose washing machine, boilers and other water-reliant appliances are in tip-top shape, and one where they constantly keep clogging up and need replaced.

Hard water is caused by the presence of minerals like magnesium and calcium. While they both can be beneficial for human health, they certainly aren’t for some of your household appliances and pipework.

Devices like water heaters can start working sluggishly and well below their stated efficiency levels because of the mineral deposits that build up over the years. This may have multiple negative effects like:

  1. Increased electricity bills
  2. Repair bills
  3. Reduced lifespan of the appliance
  4. Increased water bills
  5. Decreased water pressure

As luck would have it, devices do exist which transform the troublesome hard water which pipes deliver to your home into water that’s not only much kinder on your appliances, but more effective when it comes to washing dishes, cleaning clothes etc.

In this guide we’ll examine what hard water and its hazards are, as well as taking a look at how a water softener works and how it may benefit you. 

We’ll also cover some essentials you should be aware of as you go shopping for a new water softener. The things you should keep in mind when picking one out that’s ideal for your particular situation.

water softener system

A typical water softener system

What is hard water and why is it trouble?

What you first need to understand is that the compound known as water is never absolutely pure in nature – you’ll never find a natural body of water comprised exclusively of hydrogen and oxygen atoms.

As water is unquestioningly the best and most versatile solvent on the planet, it’s understandable that it picks up impurities, both underground and on the surface. One of the most common ones is carbon dioxide. Although it isn’t hard in and of itself, carbon dioxide enhances water’s solvent properties even further when present.

shower water

As it makes its way through countless underground rivers and streams, fresh water picks up a broad array of elements and impurities. Most harmful ones are dealt with in water treatment facilities, but these do nothing to eliminate water’s innate hardness. This hardness can be defined as the relative concentration of metal cations in a given amount of water. Magnesium, calcium, manganese and iron make up the vast majority of these metals.

Quick Definition: a cation is an ion with a positive charge (it has lost an electron).

From a biological standpoint, hard water is perfectly safe for human consumption, but less so for the use in our appliances. The problem is more widespread than one may think – water surveys conducted in the United States suggest that hard water affects almost the entire midwest and eastern parts of the western US, all the way from Montana to Texas.

mineral deposit in pipe

Mineral deposit in pipe

Besides hampering household appliances, hard water is bothersome in other ways too. It reduces the effectiveness of both liquid and solid detergents and leaves stains on dishes, windows, and other surfaces which are unseemly and hard to get rid of (see how to remove them here). It can cause irritation of one’s skin since soap that would otherwise be rinsed off while washing tends to create a fine film on it and prevents the skin from returning to the slightly acidic state it’s naturally in.

hard water stains

Hard water stains

If you aren’t sure whether water in your home is hard or not, there are home-use water testing kits you can purchase to find out. These are available in hardware store and online from sites like Amazon and Home Depot. Once it turns out that you do in fact have hard water, it’s high time something be done about it. The answer – water softeners!

How do water softeners work exactly?

The appliance we know as a water softener consists of two tanks which are connected to your home’s plumbing system. Depending on the softener’s capacity and intended use, it is typically installed either as close to your home’s water entry point as possible, or underneath the sink in case you’re only getting a smaller one to use in the kitchen.

Regardless of its size, the water softener relies on the fact that the metal ions hard water carries (magnesium, calcium etc.) all have a positive charge. Since the water is hard on a molecular level, the only course of action is to replace the hard metal ions with ones which are also positively charged, but do not cause mineral build-up. The softener’s tank is precisely where this replacement takes place during a process referred to as ion exchange.

This substance that performs this process is called the ion exchange resin. The resin is high in sodium ions which are ready to do a trade with the hard water ions.

Ion exchange resin beads

Ion exchange resin beads

As water that has a high concentration of magnesium and calcium ions (hard water) comes into contact with the resin, the hard water ions bind to the resin and are replaced with the sodium ions. Like the name suggests, there is an ion exchange.

Sodium & calcium ion exchange

Sodium & calcium ion exchange

What’s left is water that is noticeably softer. While there is indeed some sodium left in this soft water, its concentration is so small that it can be considered negligible.

This process has proven to be very effective, but it also has its limits. Sooner or later, all of the sodium ions which the resin holds onto are going to be depleted and the ion exchange process will stop.

That’s where the softener’s second tank comes in. This tank is where softening salts are stored. Softener salt is made of potassium chloride or sodium chloride. This tank holds brine (salt water) that is rich in the same sodium ions used in the resin.

Now the process is reversed – the brine, which has a greater salt concentration than ordinary salt water, is pushed into the softener’s main tank and is used to thoroughly rinse off the undesired metal ions which are then flushed down the drain. The resin beads are then refreshed and can make their magic once more.

This second process is known as regeneration. It takes a while to complete, so the water softener is usually set up to initiate the regeneration process at night. The good models will actually do this automatically at a time which is convenient (or when it’s needed) and they will only use the exact amount of water needed.

Are there water softeners that don’t use salt?

Salt-based water softeners are very effective at what they do, but they aren’t without their drawbacks. Buying special salt can be expensive if you have a large household, and disposing of salt water down the drain isn’t good for the environment. Although ion exchange water softeners are by far the most widespread, other types of softener do exist. 

The first is a kind of water filtration system which uses no salt in its operation. It relies on another fancily named process, chelation, to keep the metal ions in the water from adhering to surfaces.

salt-free water softener

With this solution, you’re getting water that’s basically as hard as it was before with some of the same problems that plague it like forming curds instead of soap suds. On the other hand, it has been shown that water which passes through these salt-free “softeners” doesn’t leave as much metal residue behind as regular water, so buying one is definitely an improvement over not using any kind of softening method.

To summarize, the water that is treated by a salt-free system is conditioned and not actually softened. It still contains the hard water minerals, it’s just that they are inhibited from bonding with surfaces and forming deposits. That means the water shouldn’t form scale on pipes and heating elements, but it doesn’t solve the problem of soap lather being able to form.

A nice touch with some of these systems is that they can actually remove existing mineral deposits too. This isn’t possible with salt-based models.

Even more controversial are devices which use magnetism and electricity to descale water. They have coils which you attach to the outsides of your pipes. Once turned on, they give the pipe a negative charge which supposedly halts positively charged ions in their tracks and descales the water. This method remains scientifically unproven as of yet. However, anecdotal evidence suggests that there are satisfied customers out there.

These systems give the same result as those that use chelation. They condition the water, rather than actually soften it.

Water hardness in USA

Water hardness in USA

What to look for in a new water softener?

After reading everything mentioned above, you might be considering a water softener of your own, or it may be time to retire your old one. Whatever the case may be, here are a few items to consider when shopping for one. 

  • Capacity

The softener’s capacity will probably be your chief concern. It’s a bit tricky to blindly gauge how big the unit should be, but there are ways to narrow your parameters.

First, consider the type of household the softener is going to be installed in. How many people live in it? What are their water consumption habits? There are calculators online which you can use to determine your household’s daily water consumption as well as the average consumption of each member with a good amount of accuracy.

Once you know how much water you use daily, getting a softener which can meet those needs should be a snap.

  • Water Hardness

You need to know your maximum water hardness, so that you can choose a softener unit that is capable of treating the water effectively. Water hardness is measured in grains per gallon (gpg) and can be easily tested using an inexpensive kit. These are available at your hardware store and online from stores like Amazon.

The size of a water softener should be based on your water hardness and the amount of water that your household uses on a daily basis.

For example, water hardness of 10 gpg and a 3 person household would probably require a 32,000 grain softener.

Water of 45 gpg hardness and a 5 person household would require something more like a 96,000 grain softener.

  • Flow Rate

Tied closely to capacity, a water softener’s supported flow rate indicates how much incoming water it can handle at any given time. You can determine the flow rate with a special meter or by hand. If you’re doing the latter, it’s easiest to take a marked container and a stop watch. Start filling the container with water and stop after a minute has passed. The amount of water inside the container after one minute is the same as your flow rate. Some entry-level softeners may not be able to keep up with a good flow rate, so keep that in mind when choosing.

  • Regeneration Control

Regeneration is the name given to the process where the salt water stored in the brine tank is used to rinse the ion exchange resin. This resets the resin and cleanses it of hard water ions, ready to start working like new again.

Regular regeneration is crucial to keep the water softener working as intended, and there are a couple of different ways it can be controlled. The most basic one is a built-in regeneration timer. This method simply tells the softener that it should start the regeneration process at a given time, usually in the dead of night. While this ensures that you always have soft water at your disposal, it can be costly – replacement salt is used up each time recharging is initiated, and since this is typically on a daily or bit-daily basis, the salt goes to waste if you’ve been using less water than usual.

The smarter approach is to get a softener with DIR – demand initiated regeneration. Models that use DIR are equipped with meters which measure how much water the unit has softened and the amount of salt that’s still in it. Once this falls below a certain point, the regeneration process is initiated. This is obviously the superior method as it saves the environment as well as your money as salt usage can be drastically decreased depending on your water consumption levels.

  • Filtration

Softer water doesn’t necessarily mean cleaner water too. Oh, you’ll definitely notice a difference in taste – that harsh metallic aftertaste that can sometimes be present if you have old plumbing or access to water of lower quality is all but sure to fade away – any pollutants or harmful chemicals will remain even in soft water though.

Water softener manufacturers are aware of this and are offering combo units which include a water filtration system.

Chlorine is actually quite damaging to water softener resin, so it’s always a good idea to run a filter before the softener unit in order to protect it. Water that is high in sediment might also pose problems.

  • Certificates

Every manufacturer likes to tell tall tales about their product’s abilities. One way of validating is to look for seals of approval from recognized organizations which test them out and give their approval. The most trusted organizations which endorse water softeners are the Water Quality Association and NSF International. Although knowing that a softener has been deemed worthy by either doesn’t mean it’s the best one around, it does establish it as a trustworthy appliance.


If you enjoyed this article then you might enjoy our post about water shortages next.

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Image Sources:

By SmokefootOwn work, Wikipedia

By Bugman at English Wikipedia, Link

By Josefus2003, from Wikimedia Commons

By BbypndaOwn work, Wikipedia

Water hardness map, link

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