How Do Water Softeners Work?

Most water softeners on the market are ion exchange systems. In these systems, hardness ions (calcium and magnesium) are exchanged for salt (sodium or potassium) ions. The exchange takes place within the resin tank of the water softener. When water flows through the tank it comes in contact with small resin beads that are covered with salt ions. As water flows through the resin beads, hardness ions trade places with salt ions, hence the higher salt content in softened water.

As larger volumes of water are softened, the beads become exhausted and contain nothing but hardness ions . The beads are recharged by adding bags of salt to the brine tank. Recharging works the same as softening but in reverse. The hardness ions swap places with the salt ions in the brine tank and excess minerals are rinsed into the wastewater drain.

Demand initiated regeneration (DIR) water softeners are the most common ion exchange softeners sold locally. DIR softeners meter water usage over time and only regenerate when needed. Some softeners operate on a timer or schedule that regenerates at set increments. This older technology can be very wasteful of both salt and water because the softener will regenerate even during periods of low household water use (e.g. vacation away from home). At the same time, these models can leave you short of soft water if you have periods of higher water use (e.g. house guests).

Read our FAQ about the different types of water softeners available

Water Softener Components

Click on the component names to the right of the diagram to highlight and read more about that component.

Hard Water Supply Soft Water to House Drain Timer-and-Valve Assembly Mineral Tank Outlet Manifold Plastic Beads Brine Tank Salt Float-and-Valve Assembly

What are the differences between water softener salts?

There are generally three different types of water softener salts available:

Salt produced by the evaporation of seawater
Refined and completely purified salt, such as table salt

Rock salt is cheaper than solar or evaporated salts but contains more insoluble material. As a result, solar and evaporated salts keep your water softener cleaner. The type of salt you choose to buy will depend on the frequency of regeneration. If your water softener regenerates a lot you’ll want to use solar or evaporated salts to avoid the fast build-up of non-soluble matter from rock salt. For the average home owner this should not be a concern as excess minerals are rinsed away during regeneration.

For those concerned about the sodium content in their drinking water, potassium chloride is an alternative to sodium chloride. Potassium chloride is slightly more expensive to buy but works in the same way as regular water softening salt. Potassium chloride is safe for most water softeners but consult your owner’s manual before switching.

Read our FAQ about softened water and health

Are there alternative technologies for treating hard water?

Some retailers sell technologies meant to prevent scale build–up in household appliances without the use of salt, and sometimes even water. Most of these alternative technologies do not soften water (i.e. do not remove calcium and magnesium) but instead change the properties of suspended solids in the water to stop scale from forming on water heater elements, taps, etc. In some cases the technologies still require backwashing. Examples of these water softener alternatives are:

  • Electrically Induced Precipitation
  • Electromagnetic Water Treatment
  • Capacitive Deionization (CDI)
  • Template Assisted Crystallization (TAC)

There is currently very little information published by independent agencies to verify the effectiveness of these new technologies. A recent study published by the U.S. Water Reuse Research Foundation clarifies the effectiveness of the four technologies listed above.

Did You Know:
Although rock salt is cheaper than solar or evaporated salts, it contains more insoluble material. Solar and evaporated salts keep your water softener cleaner.
“Most water softeners on the market operate on an ion exchange system. This is where hardness ions (calcium and magnesium) are exchanged for salt ions (sodium or potassium).”