How Effective Are Ion Exchange Water Softeners at Removing Hardness From Water?

Ion exchange water softeners are the most effective common way to remove hardness from household water: a correctly sized and set softener typically brings hardness down to under 1 grain per gallon (gpg), and often to 0. On 15 gpg water, that is more than a 93% reduction, approaching 99% or more when the output tests at or near zero.

How well a particular softener performs depends on sizing, the hardness setting, the salt dose, iron in the water, and whether the resin is healthy. Below we cover how ion exchange works, what affects results, its real drawbacks, and how it compares to other methods.

How Ion Exchange Water Softeners Work

Ion exchange softeners use a tank of cation exchange resin: small plastic beads with negatively charged sites that hold sodium (or potassium) ions.

• As hard water flows through the tank, positively charged calcium (Ca2+) and magnesium (Mg2+) ions stick to the resin more strongly than sodium does.
• The resin releases sodium ions into the water in their place.
• When the resin is loaded with hardness, the softener regenerates: it rinses the bed with salt brine, which pushes the calcium and magnesium off and sends them down the drain, recharging the resin with sodium.

Because the exchange swaps out the hardness ions themselves, a softener handles both carbonate ("temporary") hardness and non-carbonate ("permanent") hardness. It doesn't matter which mineral salt the calcium came from.

What Is Water Hardness and How Is It Measured?

Hardness is the amount of dissolved calcium and magnesium in water. It's measured in grains per gallon (gpg) or milligrams per liter (mg/L, roughly the same as ppm). One gpg equals 17.1 mg/L. The U.S. Geological Survey classifies water as:

Hard water leaves scale in pipes, water heaters and fixtures, reacts with soap to form scum, and leaves spots on dishes and glass. To convert a test result, use our guide to converting hardness from ppm to grains per gallon .

 

 

How Effective Are Ion Exchange Softeners at Removing Hardness?

A working ion exchange softener removes essentially all of the calcium and magnesium it is sized for, from moderately hard water to very hard well water. What you get at the tap depends on these factors:

• Correct hardness setting. The setting should match your measured hardness in gpg, plus 5 gpg for every 1 ppm of clear-water iron. Set too low, the softener runs out between regenerations and hard water slips through. See the ideal hardness setting for your softener .
• Right size for your water use and flow. Capacity has to cover your daily hardness load, and the tank has to handle your peak flow. Running far above a softener's rated flow reduces contact time and can let some hardness through.
• Salt dose and regeneration. A lighter salt dose is more efficient but leaves the resin less fully recharged. A properly programmed demand-initiated (metered) softener regenerates when the resin actually needs it.
• Iron and fouling. Clear-water (ferrous) iron is removed along with hardness, but it slowly coats the resin. Every SoftPro softener handles clear-water iron up to 3 ppm; above that on a well, an iron filter such as the SoftPro AIO Iron Master should go in front.
• Resin condition. Chlorine in city water slowly breaks resin down over many years. Damaged or fouled resin loses capacity.

If you've installed a softener and still see hard water, the cause is almost always one of these. Our troubleshooting guide why is my water still hard after installing a softener walks through each one.

Drawbacks and Limitations of Ion Exchange Softeners

Added sodium

Softening adds sodium in proportion to the hardness removed, roughly 7.5–8 mg of sodium per liter for every grain per gallon removed. For 10 gpg water, that's on the order of 75–80 mg per liter. The American Heart Association recommends no more than 2,300 mg of sodium a day for most adults. If you're on a sodium-restricted diet, you can use potassium chloride instead of salt, bypass the kitchen cold tap, or add reverse osmosis for drinking water. More detail is in our page on water softener sodium and health .

Salt, water and upkeep

A softener uses salt and some water each time it regenerates. How much depends on hardness, water use and settings. Demand-initiated regeneration and a correct hardness setting keep both down. Routine upkeep is simple: keep salt in the brine tank, clean the tank about once a year, and test your softened water occasionally. For operating costs, see how much it costs to operate and maintain an ion exchange softener .

Brine discharge

The brine from regeneration goes down the drain. In a few areas with water reuse or chloride limits, local agencies restrict salt-discharging softeners, so check local rules.

What a softener doesn't do

A softener doesn't remove chlorine, sulfur (rotten-egg) odor, bacteria or most other contaminants. Those need a filter, UV or reverse osmosis.

Ion Exchange vs. Other Water Softening Methods

If you're weighing alternatives, read our guides to salt-free water softening systems and whether magnetic water softeners really work . For drinking water, see our reverse osmosis filters .

Choosing the Right Ion Exchange Softener

To choose the right ion exchange softener , start with these steps:

1. Test your water for hardness, and for iron if you're on a well.
2. Estimate daily hardness load: people × daily gallons per person × compensated hardness. For example, 4 people × 75 gallons × 15 gpg = 4,500 grains a day.
3. Choose a size that covers several days of that load and your peak flow. Our how to size your water softener guide and the calculator below do the math for you.
4. Look for demand-initiated regeneration and a bypass valve for easy maintenance.

The SoftPro Elite Smart HE is a salt-based, high-efficiency ion exchange softener with demand-initiated regeneration, available in 32K, 40K, 48K and 64K. You can compare all our models in our water softener systems collection.

Frequently Asked Questions