Water softeners are large floor standing units that use ion exchange resins in the form of beads to exchange hard minerals, (usually calcium and magnesium) with soft minerals including sodium or potassium. As the softener is used, the sodium or potassium that coat the ion resin beads is replaced with calcium and magnesium. Eventually the resin beads become saturated with magnesium and calcium, requiring a backwash to remove the calcium and magnesium that has saturated the ion resin beads, and then a regeneration process where the ion resin beads are saturated with sodium or potassium so that the ion exchange cycle can continue.
To regenerate the ion resin beads, sodium or potassium crystals are added to a tank that creates a brine that through a regeneration and backwash process donates sodium or potassium to the ion resin while washing the absorbed calcium and magnesium down the drain. Some softeners feature a programmable timer that regenerates the ions and remove the absorbed hard minerals at prescribed intervals, while more modern units sense when the ion resin requires regeneration, automatically backwashing and regenerating when needed.
Hard water is usually found in deep wells, and is rarely a problem with municipal water supplies. Due to the excessively high levels of calcium (lime) and magnesium, hard water causes mineral build-up in showerheads, dishwashers, pipes, and water heaters, reducing water flow. In addition, soap and detergent lathering is reduced causing less effective cleaning, leading to soap scum on glasses and dishes and lime deposits on bathroom fixtures, toilets and bathtubs. Soft water feels more slippery, creates more lather with soaps and shampoos, and makes it more difficult to wash soaps and shampoos from your hair and skin.
The majority of water softeners use sodium chloride, however many new water softener manufacturers offer potassium chloride as an alternative. While water with potassium is safer than water with sodium, excess potassium can also be dangerous. Drinking, making coffee or juice, or cooking with softened water is not recommended.
The high sodium or potassium content of softened water can harm grass or vegetation and cause more frequent regenerations due to the depletion of the sodium or potassium crystals due to the high water volumes. More frequent regenerations also result in higher water softener operational costs, as the sodium or potassium crystals will need to be added more often. Softened water should only be used for washing and cleaning.
As the level of sodium is higher in softened water, it should not be consumed by those with hypertension (high blood pressure), congestive heart failure or kidney disease. While water softeners should only be used to treat microbioligically safe water, softened water is not recommended for drinking without removing the potassium or sodium that has been added. The only effective method of removing potassium or sodium from softened water is by distillation or reverse osmosis.