How a Water Softener Can Affect Your Water Heater?

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Water heaters are an expensive investment, so anything you can do to protect your heater and extend its lifespan is completely worth it.

You might have heard that installing a water softener system could have a few benefits for your water heater, too. But what about the theory that softened water might cause corrosive damage in your heater? Is this true?

Here, we’ve shared the effects of a water softener on a water heater.

📌 Key Takeaways:

  • Soft water prevents hard water mineral damage inside a water heater, which should extend its lifespan and maintain its efficiency.
  • However, naturally soft water may also corrode the water heater anode at a faster rate, which could shorten its lifespan.
  • It’s better to use salt-softened water from an ion exchange system (which doesn’t have corrosive properties) than hard water in a water heater.

🔎 2 Benefits Of Water Heater With Water Softener

Let’s take a look at the benefits of installing a water softener system upstream of your hot water heater.

Prevents Scale Damage

A water softener removes calcium and magnesium minerals from water, replacing them with sodium ions in a process called ion exchange.

Hardness minerals leave yellowish-white deposits on surfaces that come into contact with water. These deposits are known as scale.

Limescale is incredibly damaging to pipes and plumbing fixtures. It reduces water’s flow rate and accumulates quickly, potentially leading to cracks and blockages.

If you have hard water, all your water-using fixtures and appliances will be affected by limescale buildup, including your water heater tank.

👨‍🔧 By softening your water in a water softener, you eliminate scale altogether, so you don’t have to worry about the damaging effects of mineral buildup in your hot water heater.

Preventing limescale damage on water heater element

Maintains Efficient Heating Performance

Because a water softener system removes scale-causing minerals, it prevents scale damage to your water heater tank.

Over time, layer upon layer of limescale accumulates in a hard water-using water heater. These layers act as insulation, meaning that the heating elements have to work for longer to heat up the water to the desired temperature. A longer heating time means a less efficient performance.

On the other hand, if you install a water softener in your home’s point of entry, your water heater won’t be affected by limescale at all, meaning that your water heater should maintain its efficient performance throughout its lifespan (hopefully 10+ years).

👉 Protect Your Water Heater with the Best Water Softeners

🧐 Does Softened Water Corrode Water Heaters?

You might have heard that there’s a link between soft water and corrosion.

But – importantly – only naturally softened water has corrosive properties because it has a low pH and often has low TDS, making the water “hungrier” and more open to leaching metals and other materials from plumbing fixtures.

Water heaters are fitted with an anode rod, which absorbs the water contaminants that are most likely to corrode the tank.

Because naturally soft water is corrosive, it will corrode the anode rod at a faster rate. Eventually, the anode may be unable to protect the tank, and the tank’s metal lining will begin to corrode.

You’ll need to replace the anode rod more frequently to avoid major damage to your heater.

You won’t experience this issue with salt-softened water, which doesn’t have corrosive properties because its pH and TDS levels are higher.

Scale deposits and buildup on water heater

The Softened Water Heater Corrosion Misconception

So, why is there a misconception out there that salt-softened water corrodes water heaters?

According to this report, it seems to stem from plumbers misdiagnosing the cause of heater problems as corrosive water, partly due to the use of aging prediction tools like the Langelier Saturation Index (which was never designed to be applied to any kind of softened water, natural or otherwise).

The Langelier Saturation Index hypothesizes that a thin layer of limescale can protect against corrosivity. However, the same report indicates that limescale might actually exacerbate corrosion due to the formation of crevice formation and bacteriological activity.

Further, the report notes that there are other causes of corrosion in water, including aluminum, iron, and manganese, and these impurities are removed by an iron exchange water softener – suggesting that installing a water softener might actually protect against corrosion.

There was also a study conducted in Loughborough, UK, which investigated the difference between corrosion in water heaters when using a hard vs salt-softened water supply.

The study found “no significant difference” between the rate and level of corrosion between the water heater using hard water compared to the unit using soft water. This further supports the notion that softened water is no more corrosive than hard water.

🆚 Should You Use Hard Water Or Soft Water In A Water Heater?

So, is it better to use hard water or salt-softened water in your water heater?

We highly recommend using soft water from an ion exchange system. Why? Because soft water from a water softener won’t leave damaging scale deposits in your water heater, and nor will it cause corrosive damage like naturally softened water. This will extend the life of your water heater and keep it in good working condition for as long as possible.

Keep in mind that water heaters are made from metal and constantly heating water, so it’s normal for them to corrode eventually (usually after 8-12 years). There will be a time when you need to replace your water heater, regardless of what water you use.

In any case, make sure to get your water heater inspected frequently, so you know it’s working as it should be.

Hard water vs soft water comparison chart

📑 Final Word

Now we know the theory that salt-softened water is corrosive is just that: a theory. There’s actually more evidence to support the fact that water softeners can help protect against corrosion by removing impurities with corrosive abilities, like iron and aluminum.

So, what can you do if your water heater manufacturer tries to negate your heater’s warranty because you’ve installed a water softener in your home?

We recommend sending the manufacturer a link to the report shared in this guide and summarizing the arguments against the “softened water is corrosive” misconception. Hopefully, this should support your argument that your water heater’s degradation (if it happens) isn’t caused by your water softener.

❔ How a Water Softener Can Affect Your Water Heater: FAQ

Does a water softener ruin a water heater?

A water softener doesn’t ruin a water heater. Salt-softened water from an ion exchange water softener system shouldn’t cause this issue because it has a higher pH and TDS concentration. However, naturally soft water may damage the anode rod in a water heater so much that the heater tank itself starts to corrode. Undetected, this could cause the softener to stop working before its predicted average service life comes to an end.

Can a tankless water heater be used with a water softener?

Yes, you can install a water softener system if you have a tankless water heater. In fact, many plumbers recommend water softeners to folks who have tankless water heaters because softened water prevents mineral buildup in the entire heater unit, which affects its energy efficiency, shortens its average service life, and makes it more expensive to run. You’ll still need to get your water heater inspected regularly, and follow your plumber’s advised water heater maintenance.

Can salt from water softener damage water heater?

No, there’s no evidence to suggest that salt from a water softener system could damage your water heater. You might have heard that soft water is more corrosive than hard water, which means it corrodes the water heater’s anode rod at a faster rate. If the anode becomes too corroded, the tank itself will start to corrode, leading to the water heater eventually failing. However, this only applies to naturally softened water – salt-softened water from an ion exchange water softener does not have corrosive properties and shouldn’t damage your water heater.

Should hot water be softened?

Yes, ideally you should soften the hot water as well as the cold water in your home. Softening your hot water means your entire home’s plumbing, including your water heater, will be protected against hard water scale. That means you’re getting the best value from your investment.

  • 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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