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Does Soft Water Help or Hurt Water Heaters?

Does Soft Water Help or Hurt Water Heaters?

By Jon Briggs

Soft water helps water heaters last longer!

Soft water kills water heaters!

Which one is true?

Liked many things in life the answer is, “It depends.”

Ion Exchange Softeners sound fancy but basically they’re the ones that use salt. Hard water is water that contains high amounts of Calcium and Magnesium. To “soften” the water hard particles are replaced with salt (sodium and potassium).

Soft water isn’t corrosive by itself. Hard water isn’t corrosive by itself.

So WHY is my water corrosive?!

We have to understand two more things first. TDS and PH

TDS means Total Dissolved Solids. So high or low TDS is measuring the amount of dissolved particles in water. High TDS water means the water is less aggressive and low TDS water means it’s more aggressive. The measurement seems backwards because low means more and high means less.

WHY?! Let me try and explain.

When water has fewer dissolved solids (less than 50 mg/L) it attempts to balance out by looking for solids around it. It just happens that it can find solids in your pipes or water heater or whatever is available. So think about it as a measurement of hunger. Low means the water is starving or it hasn’t had enough to eat so it’s aggressively looking for something to fill it’s belly!

High TDS water (more than 500 mg/L) has had plenty to eat. As a human having plenty to eat means you have plenty of energy to do stuff. That’s not a bad way to think about high TDS. Over 500 mg/L means your water has energy. That is expressed in the fact that it is able to better carry an electrical current. That is called your waters conductivity. That conductivity has the potential to dissolve away you’re your pipes by carrying an electrical charge that corrodes galvanized steel.

So, high and low TDS can dissolve your pipes.

You’re looking for that sweet spot of a TDS greater than 50 but less than 500.

pH stands for “potential of Hydrogen” but in simpler terms its measuring how acidic water is. Again the words we use to explain the measurement might seem backwards because low means high acid and high means low acid. Same thing here. The lower the pH the hungrier the water is and It’s looking to eat.

The sweet spot for pH is 7.

So with all that said we’re back to the same question, “Why are we replacing water heaters so often?”

Well, a salt based softener won’t lower pH or TDS so that’s not the reason.

Conversely a salt based water softener can definitely raise the Total Dissolved Solids (TDS) maybe that’s the culprit. The higher TDS isn’t because it’s already dissolved your pipes. The increase is because the softener added sodium ions so the water is more electrically conductive.

Just like in high school science class when you made a battery with galvanized washers and copper then added an acid! Higher salt—better acid.

Water that’s softer than 25 gpg probably won’t make the TDS high enough to worry about but water higher than 25 gpg will definitely do so!

For example, water in Bountiful, Utah is almost always above 25 gpg and in lots of cases it’s as high as 37. Soften that water too much and you have a big problem. Just drive around Bountiful sometime and you’ll see the corpses or water heaters laying beside the road. Check with the owners and you’ll usually find that these water heaters have only been in service a couple years. They’re wearing out fast! Why?

Well, the reason could be that terribly hard water was untreated and scale formation significantly reduces the longevity and energy efficiency of the water heater OR Softening the water to protect it against scale formation backfired on you! If that water is very hard, is highly alkaline, or has a low pH it can be corrosive after softening.

Bottom line? You have to know your water. Really know it. Regular titration tests seem to always get the hardness wrong. You’ll have to either send it to an expensive lab or a better idea is to call RETEGO and really know your water!


This article is a simpler version of an article written by Greg Reyneke.