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Filling glass of tap water

How Water Softeners Work

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Water softeners are a common fixture in houses and buildings of all shapes and sizes. Many people know that they need to refill it with salt every now and then, but let’s take a look at why.

What is Hardness?

When we talk about water hardness, it’s not like we’re saying the water will come out of your faucet as a chunk of room-temperature ice. Hardness refers to the amount of calcium and magnesium that the water has in it. It picks up these minerals as it journeys through soil, filters at the purification center, and even pipes.

These minerals make soap less effective, and can lead to spots on laundry or cars. Most importantly, the minerals can build up as thick scales that can destroy appliances.

Getting Rid of the Minerals

Even the best filter won’t catch all the calcium and magnesium, and even if one could, it would get quickly clogged. So instead of filters, your water softener uses an ion exchange system.

The mineral tank of your softener is filled with plastic resin beads that have a negative charge. A brine, or saltwater, is run through these beads, also known as water with sodium chloride. If you remember your chemistry, sodium is a positive ion, or Na+. Like magnets, the negative charge on the beads grabs the sodium ion.

Now here’s where the calcium and magnesium are removed. Both of these are also positive ions, Ca++ for calcium and Mg++ for magnesium. Those extra pluses aren’t just for looks. They mean that the calcium and magnesium ions have a stronger charge than the sodium ions. So when hard water is run through the beads, the stronger ions grab onto the resin beads and kick the sodium off into the water.

The result is soft water without calcium or magnesium in it. It does have a small amount of sodium in it, which can be rough for people on a low-sodium diet. In those cases, they should use a potassium chloride softening system. These cost three to four times as much, but don’t put sodium in the water.

But Why Do I Keep Adding Salt?

After a while, the resin beads in your mineral tank will get fully saturated with calcium and magnesium, which means they won’t soften your water. Remember that saltwater from earlier? When you add salt to the brine tank, you create a reserve of saltwater that’s used to recharge the resin beads. The saltwater is flushed through the resin beads. The sheer volume of sodium ions knocks the calcium and magnesium ions off the beads and takes their place. The result is a bunch of hard water, which is flushed down the drain, and resin beads that are full of sodium ions and ready to soften water.

With older systems, this was often controlled by a timer that you had to set, but many modern systems have automatic recharge cycles and sensors that are based on the initial hardness of your water. All you have to do is periodically add salt, and the computer takes care of the rest.

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