How Do Water Softeners Work?

By: Nicholas Gerbis  | 
Marshall Brain
Marshall Brain explains how water softeners work.

We call water hard if it contains a lot of calcium, magnesium or other minerals. Soft water, on the other hand, is called that because it has lower concentrations of these minerals. But how do water softeners work?

Groundwater acquires these hard water minerals by dissolving them from surrounding soil and rock. The industry measures water hardness in terms of grains per gallon (GPG) or milligrams per liter (mg/L). A grain is defined as 64.8 milligrams of calcium carbonate.


If your water supply tests at 1 GPG (17.1 mg/L) or less, then you have soft water. A water softener works by exchanging the calcium and magnesium ions in hard water with sodium or potassium ions, effectively reducing mineral content and softening the water.

Why Get a Water Softener?

How do all those numbers affect you? Hard water causes two problems:

  1. Dissolved calcium and magnesium precipitate out of hard water as scale, which builds up on the insides of pipes, water heaters, tea kettles, coffee makers and industrial machinery. Scale reduces flow through pipes and is a poor conductor of heat. Eventually, pipes can become completely clogged.
  2. Hard water reduces soap's ability to lather, whether in the shower, sink, dishwasher or washing machine and reacts with soap to form a sticky scum.

You can combat hard water in various ways, including filtering it by distillation or reverse osmosis, adding a packaged chemical softener such as powdered borax or washing soda (sodium carbonate) or running it through a water softener.


Filtration in sink taps and refrigerator water dispensers improves water's taste, but its steep price tag makes it impractical as a household solution. Packaged chemicals soften water in small batches, such as washing machine loads, but render the water undrinkable, take a toll on clothes, and, in some cases, contain phosphates that harm the environment.

With all this in mind, it's clear why water softeners are so popular: They remain the least costly and most effective way to rid your water of troublesome minerals.

In the next section, we'll take a peek inside a water softener and find out why plastic beads aren't just for Mardi Gras.


Turning Hard Water Soft

Water softeners operate on a simple principle: Calcium and magnesium ions in the water (hard water minerals) switch places with more desirable ions, usually sodium. The ion exchange process eliminates both of the problems of hard water because sodium doesn't precipitate out in pipes or react badly with soap. The amount of sodium this process adds to the softened water is quite small — less than 12.5 milligrams per 8-ounce (237-milliliter) glass, well below the standard set by the Food and Drug Administration for very low sodium. If you have health concerns, discuss them with your doctor or consider either using a different kind of softener or only softening wash water.


Brine Solution, Resin Beads, and Sodium Ions

The ion replacement takes place within a tank full of small polystyrene beads, also known as tiny resin beads. The negatively charged beads are bonded to positively charged sodium ions. As the water flows past the beads, the sodium ions swap places with the calcium and magnesium ions, which carry a stronger positive charge.

So why do you load up water softeners with salt if the plastic beads do all the work? Over several cycles, calcium and magnesium replace all of the sodium in the beads, after which the unit can no longer soften water. To fix this problem, the softener enters a regeneration cycle during which it soaks the beads in a strong solution of water and salt — or sodium chloride salt.


The sheer amount of sodium in the brine solution generated in the brine tank causes the calcium and magnesium ions in the beads to give way, and the beads are recharged with sodium. After the regeneration process, the water softener flushes the remaining brine, plus all of the calcium and magnesium, through a drainpipe. Water softener regeneration creates a lot of salty water — around 25 gallons (95 liters).

Most home water softeners use the plastic bead and salt approach. The main difference between them is how they decide when to regenerate. Some softeners use electric timers that flush and recharge based on a regular schedule. Others use a computer that judges bead depletion based on water use. Still, others use a mechanical water meter to measure water use and kick off the recharging process only when sodium exhaustion requires it.

Each approach comes with its share of pros and cons. Electronic timer units can't dispense soft water while recharging. Conversely, some computerized systems carry a reserve resin capacity, so you can tap them for a squirt or two of soft water even during recharge cycles. Most flexible of all are mechanical systems, which come equipped with two mineral tanks. One tank can make soft water while the other recharges.

High-efficiency water softeners run between $500 and $6,000 and are designed to be easy to install and remove, which is good news if you want to take your unit with you when you move. However, unless you are confident in your electrical and plumbing abilities, you might want to hire a plumber to get a softener installed. Some stores include installation with the purchase of a water softener.


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