How do water softeners work?« Back to Questions List

You might have heard about water softeners being used in many residences. These are very common at houses whose source of water is well or that the ground water is very hard. You know what hard water is. Sometimes the ground water may contain many minerals especially calcium, magnesium, iron etc. Such water is classified as hard water. The disadvantages of using hard water are that they gradually clog the pipes, form scales in the bath rooms and kitchen sinks. Also soaps and detergents do not lather well with hard water. In such cases, the water is softened using water softeners before being used.

The water softener removes the calcium and magnesium present in the water by using plastic beads and cleans itself periodically by a process called regeneration. There is a mineral tank in which filtration happens (removal of Ca and Mg) using plastic beads made of polystyrene. How this happens is because opposite charges attract. Calcium and Magnesium are positively charged and the plastic beads are negatively charged. Application of small current deposits the minerals on beads. Thus the minerals get removed from the water molecules.

Now, there is a need to clean the plastic beads once in a while (regeneration). To accomplish this, there is a control valve which is programmed using a timer to decide at what interval, the beads have to be cleaned. As a first step, the water flow is reversed to flush the debris out of the tank. Then brine water (highly concentrated with water) is pumped from a brine tank into the mineral tank. 

 
Instead of sodium, potassium is being used in the brine tank for health reasons. The potassium is positively charged. It is attracted to the plastic beads. Because its concentration is very high, it forces calcium and magnesium off the beads. The excess water is now pushed out of the tank into the drain. Then the mineral tank is rinsed many times and the salt concentration on the beads gets diluted. This diluted potassium salt gets suspended in the water as the tank starts to filter calcium and magnesium that attaches itself to the beads. 

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