Removing Iron With A Water Softener

Can a water softener be used to remove iron from water?  The answer is yes - but it's complicated! And because it's complicated, there's a lot of misinformation that exists in the marketplace - both online and with conventional water treatment dealers.

So what's the deal with iron? How do I know if a softener will remove the iron in my water? The key to understanding how well a water softener will remove iron is to understand some key bits of info about your water chemistry: iron, total hardness, and pH.

pH - Ignore At Your Peril

If there's a hidden secret to knowing how well a water softener will remove iron, it's pH. But to understand the important role pH plays, we first need to understand a little about the chemistry of ions.

An ion is a charged particle. It can have a positive or a negative charge it doesn't matter - if it has a charge, it's an ion. When substances dissolve in water they are either ionic or non-ionic dissolved substances. Sugar, as an example, dissolves in water as non-ionic substance (it has no charge). Common table salt, however (Sodium Chloride) dissolves as an ionic substance - the sodium and chloride break apart with each particle carrying a charge. The sodium carries a positive charge and the chloride carries a negative charge.

Some substances that are placed into the water will dissolve into their ions no matter what the water conditions are. But some substances are sensitive to other water conditions, and may or may not dissolve as ions depending on the conditions. The most important of these factors is pH.

The pH of the water will affect whether or not some substances dissolve into ions. Usually, an acidic pH (below 7) will encourage substances to dissolve as ions and a basic pH (above 7) will prevent substances from dissolving as ions. This is important as it relates to water softeners because they are ion-exchange technologies. Water softeners will only work on ions.

So the key to knowing how well a softener will remove iron is all about understanding the pH. If the pH is acidic the iron will exist in the water in its ionic form, and the softener can easily remove it. However, if the pH is basic, the iron will exist in a non-ionic form and the softener will have more difficulty removing it.

Removing Iron at High pH

If the pH of your water is above 7 (basic) and you have iron in your water that you want to remove with a softener - don't worry - all is not lost! But there are extra conditions to pay attention to if you want to ensure that the iron in your water will be fully removed.

The first thing to consider is that iron can exist in water in two major forms - clear water iron and precipitated iron (aka particulate iron). Clear water iron is just as it sounds: if you run a faucet for a few minutes the water will be clear and colourless coming from the faucet, even though it does contain iron. Precipitated iron, on the other hand, causes the water to run an immediate red / orange / brown colour even if you run the faucet for several minutes.

A Water Softener Will Only Remove Clear Water Iron

If your water contains precipitated iron there is not a softener that exists that will remove it. Your water will require a dedicated iron water filter to remove this kind of iron no matter how much or how little is present.

If your water contains clear water iron, and your pH is above 7, the next condition that's important to know is that the ratio of hardness to iron is very important.

Hardness To Iron Ratio for Basic pH Water

When the pH is above 7 and clear water iron is present in the water, a softener can still be used to remove the iron. However, for every 1 mg/L of iron (same as ppm) that you want to remove, you need to have 5 grains per gallon (85 mg/L) of hardness present in the water. The chemistry that is involved here is more complicated than can be explained in this article. The principle is that the hardness that's present assists the softening resin in capturing the dissolved iron. Here's an example to illustrate the how the ratio works:

Incoming water contains 15 grains per gallon of hardness

Incoming water contains 2.0 mg/L of iron

pH = 7.5

Since the pH is above 7 (basic) we know that the water needs to contain 5 grains per gallon of hardness for each 1.0 mg/L of iron that's present. So in this example, since the water contains 15 grains per gallon of hardness it could remove 3 mg/L of clear water iron. The iron concentration is 2.0 mg/L so it should all be removed.