What Do Water Softeners Remove?

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Water softeners use a process called ion exchange to produce soft water. Specifically, the process is known as cation exchange because it removes cations (positively charged ions) from water. The two cations that are primarily removed in water softening are calcium and magnesium.

Here, we’ve shared which impurities are reduced or removed by water softening. Some of them might surprise you.

What Do Water Softeners Remove

🔮 Calcium and Magnesium

Removal %: Up to 100%

First and foremost, a water softener is used to produce soft water, and that means removing the minerals associated with water hardness: calcium and magnesium.

These two minerals can be greatly reduced or completely removed by a water softening system. Preventing limescale from being precipitated in your pipes.

We’ve tested the SpringWell WSSS, a salt-based water softener and iron filter for well water. Our test results show that this system reduced over 97% of magnesium and calcium ions in our water, so it did a great job of tackling water hardness.

Calcium and magnesium are healthy minerals that humans need in trace amounts to survive.

But you can find much more plentiful concentrations of calcium and magnesium in your diet. Dairy products, nuts, legumes, and fortified juices and cereal products, are good sources of either calcium, magnesium, or both.

If you’re really concerned that you’re not getting enough of these trace minerals, consider using a supplement. But it won’t make much of a difference whether or not they’re present in your water

Healthy minerals found in water

🪨 Iron

Removal %: Up to 100% (of soluble ferrous iron in concentrations less than 3 PPM)

If your water supply contains low iron levels (1-3 PPM) alongside hardness minerals, you can also use a water softener to reduce this metal.

The same ion exchange process is used to attract iron to the resin bed. Each iron ion is exchanged with a sodium ion to ensure the water’s charge remains balanced.

So, water softening systems can remove iron – but only in its soluble form (ferrous iron).

Insoluble ferric iron can’t be removed with ion exchange, although most water softeners come with a sediment pre-filter, which will trap low levels of iron in this form. If your water contains high concentrations of ferric iron, another technique should be used upstream of the softener, like aeration or chemical injection.

We also don’t recommend using a water softener without pre-treatment if your water supply contains more than 3 PPM of iron, which could foul the resin and cause irreversible damage.

In our own testing, our water contained 2.37% PPM of iron, and 100% of this was removed by the WSSS.

However, because the WSSS also uses an iron filter that’s installed upstream of the softener, it’s highly likely that this system removed the iron before the water was softened. For that reason, we were unable to specifically measure the softener’s iron reduction abilities.

Spring well stain removal

🔩 Some Metals

Removal %: 50-100%

The primary cations in water, and those that are given the most attention in water softening, are calcium and magnesium (along with low levels of iron). But there are a handful of other common cations that may also be reduced to some extent, although with no guarantee of complete removal, by water softeners.

These cations include:

  • Aluminum
  • Barium
  • Chromium
  • Copper
  • Lead
  • Manganese
  • Mercury
  • Silver
  • Strontium
  • Zinc

In our testing of the SpringWell WSSS, our soft water contained 94% less barium and 56% less copper. Total chromium had also been completely removed, nickel was reduced by 90%, potassium by 89%, strontium by 98%, and zinc by 41%.

However, we should point out that the WSSS combines the SpringWell Salt-Based Water Softener with the SpringWell Iron Filter, so we can’t say for certain that the water softener alone was responsible for these metal reductions.

The Order of Attraction

You might be wondering why water softeners don’t remove these other cations as effectively as they remove calcium and magnesium.

For instance, you can see in our own test results that the SpringWell WSSS removed more than 97% calcium and magnesium, but the likes of selenium, zinc, and selenium were only removed by around 50%.

The answer to this, in part, lies in the theory of “order of attraction”.

When looking at the naturally occurring cation exchange process in soil, we know that the greater a cation’s positive charge, the more tightly bound it’ll be to the negatively charged soil colloid.

The same goes for synthetic cation exchange in a water softener: the greater the cation’s charge, the more attracted it’ll be to the negatively charged resin beads.

Calcium and magnesium both have two positive charges, so they’re bound more tightly to the resin than cations with single positive charges, like copper, lithium, and potassium.

However, many other cations also have two positive charges, and our theory is that we saw a greater reduction of magnesium and calcium ions purely because these were present in the highest concentrations.

There was 56 PPM of calcium in our pre-treated water, but only 0.2 PPM of copper, 0.1% zinc, 0.02% selenium, and so on.

Ion exchange process
How Ion Exchange Takes Place in A Water Softener System

🧂 Do Water Softeners Remove Sodium?

The most popular catalyst for cation exchange water softening is sodium. Sodium ions from the resin tank exchange with calcium and magnesium ions, ensuring that the water’s charge is balanced once these minerals are removed.

For that reason, water softeners don’t remove sodium from water – the softened water actually contains increased concentrations of sodium ions.

However, if you used potassium instead of sodium in your water softener, potassium ions would again be exchanged primarily with calcium and magnesium ions, but they could also exchange with some of the sodium in your water, reducing it to some extent.

We have no way of proving this because we’ve only ever tested a water softener using sodium, so we can’t confirm with our own data whether using a potassium-loaded resin would help reduce water’s natural sodium levels.

🚫 What CAN’T A Water Softener Remove?

A whole house water softener is not the same as a water filter.

So, while the system removes minerals that are responsible for hardness, along with low iron levels and some other charged cations, a water softener can’t remove chlorine, fluoride, lead, or PFAS, and it doesn’t address poor tastes or odors.

If your water contains any of these contaminants, you will need to install a separate water filtration system to address any associated water quality concerns.

Lead leaching in old pipes
source: United States Environmental Protection Agency (EPA)

📑 Final Word: Do I Need A Water Softener?

Thanks for taking the time to read this article – I hope I found the information you were looking for.

Water softeners are a highly effective solution for removing calcium and magnesium hardness minerals. But don’t confuse a water softener system for a water filter.

The purpose of a water softener isn’t to filter water – it’s to soften it. Softened water isn’t contaminant-free and will largely have the same taste, quality, and health properties as your original untreated water source.

Make sure you understand the purpose of water softener systems, and that the end result is aligned with your water treatment intentions.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

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