How Do Water Softeners Work?

Most water softeners on the market operate on an “ion exchange” system. This is where hardness ions (calcium and magnesium) are exchanged for sodium (salt) or potassium (salt) ions. This 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 sodium or potassium ions. As the water flows through the resin beads, the calcium and magnesium ions trade places with the sodium ions. That is why softened water becomes higher in salt content.

Eventually as larger volumes of water is softened the beads become exhausted and contain nothing but calcium and magnesium, thus requiring recharge. That is why you need to put bags of salt in the brine tank. The brine tank is either beside the resin tank or is packaged together with the resin tank as a single unit. Recharging the mineral tank works exactly the same way as softening the water except in reverse. The calcium and magnesium again swap with sodium or potassium rich solution from the brine tank, and the excess minerals are rinsed into the wastewater drain.

A “demand initiated regeneration” or DIR water softener is the most common ion exchange softener being sold locally. This system meters the water usage over time and only regenerates when needed. Some softeners operate on a timer or schedule that regenerates at set increments. This older technology can be very wasteful in terms of salt and water usage as the softener will regenerate even if it is not required due to low consumption in the home over a given time period. At the same time, these models could leave you short of soft water if you have higher consumption due to house guests, etc.

Water Softener Components

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:

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

Rock salt is cheaper than solar salt 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 depends on the frequency of regeneration. If your water softener regenerates a lot you will experience quicker build-up of non-soluble matter if you use rock salt rather than solar or evaporated salt. However, for the average home owner this will not be a concern as the excess material is washed away during regeneration.

Potassium chloride is an alternative to sodium chloride for those concerned about the sodium content in their drinking water. 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.

Are there alternative technologies for treating hard water?

Some retailers sell technologies that are supposed to prevent scale building up in household appliances without the use of salt and sometimes water. Most of these alternative technologies are not designed to “soften” water by removing calcium and magnesium, but may change the properties of suspended solids in water to stop scale from forming on water heater elements, taps, etc. In some cases the technologies will still require backwashing.

There is currently very little information published by independent agencies to verify the effectiveness of new technologies offered as alternatives to the traditional ion exchange softeners. It is hoped that results from a study to be published this fall by the U.S. Water Reuse Research Foundation (WRRF-08-06) will clarify the effectiveness of the four technologies listed below.

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

For more details and to get study results when available, go to www.watereuse.org/foundation

Did You Know:
Although rock salt is cheaper than solar salt or evaporated salts, it contains more insoluble material. As a result, 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 sodium (salt) or potassium (salt) ions.”
Water Softener Components
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
Hover over the words in the Key above to highlight the component in the diagram.