If you’ve ever wondered how water softeners work, the answer is simple: ion exchange. This process involves a special media bed that is used to exchange an undesirable substance, like hardness minerals, for something more desirable, like sodium bicarbonate.
Water softeners use a mechanically driven control valve that spreads the flow of water evenly over the top of the media bed. As the water passes through the media, calcium and other hardness minerals that were in solution in a calcium bicarbonate form are stripped out of the water and affixed to the media. Instead of the calcium carbonate, sodium ions are released. This process is why some people ask if soft water is “salty.” Technically, the answer is yes, although the sodium levels are very low (less than in most soft drinks).
Once the resin has absorbed all of the calcium and released all of the sodium, the media must be regenerated. This involves using a super-salty brine solution to bombard the media and force the calcium to let go and wash down the drain. Most of the sodium also goes down the drain. After this, the media is rinsed off, the brine tank is refilled, and the system goes back into service.
Single-tank systems normally require a bypass to be opened during regeneration so the building can be served by hard water. Multi-tank systems don’t have this problem since the non-regenerating tanks stay online.