A home water softener is an apparatus that removes the minerals in water that cause it to be hard. Hard water contains high amounts of calcium and magnesium. While some water hardness is desirable for taste and nutrition, very hard water leaves limescale, which can shorten the life of appliances and clog pipes.
A water test that shows more than 15 grains per gallon (256.5 milliliters per liter) of calcium and magnesium means the water is hard. A home water softener is generally only needed for the water that will be used for washing and bathing. It is not common to soften drinking water unless it also contains iron and sulfur, as there are no ill health effects of calcium and magnesium.
Hard water shortens the life of appliances, such as washing machines, dishwashers, and coffeemakers by making them work harder as the parts become coated with limescale. Limescale can also clog pipes, drains, faucets, and shower heads. Hard water reduces the effectiveness of soap by reducing its ability to foam and lift dirt, and the minerals bind with soap to create soap scum inside tubs and sinks. Clothing, skin, and hair washed with soft water are cleaner and softer because no mineral residue is left behind, and dishes don't have water spots after washing.
The most common type of home water softener works by an ion exchange system. The water passes over a filter made of sodium-impregnated resin beads. The beads hold the calcium and magnesium particles and release the sodium particles into the water. The beads are regularly bathed with brine in order to recharge the lost calcium.
Some water softeners work on-demand, while others are controlled by a timer. An on-demand home water softener recharges the resin beads with sodium as needed, while a timer system does the brine wash at a set time, usually at night.
Due to the increased sodium content from the ion exchange process, the taste of soft water taste can be unpleasant and salty. People with hypertension or other health conditions who require a low-sodium diet should not drink water softened with sodium. Some manufacturers recommend using potassium in place of sodium if the soft water is to be used for drinking. Other methods of water softening may be used, such as a carbon filter or reverse osmosis system, but these are not as efficient if the water is very hard.