Water softener systems remove calcium and magnesium from hard water through ion exchange, but caution must be taken as it exchanges sodium and can harm those on low-sodium diets and plants. Hard water is caused by minerals in groundwater and is measured in grains per gallon. All whole-home water softening systems use ion exchange, which captures calcium and magnesium ions and releases sodium ions. The different types of water softener systems vary in the amount of user input required for recharging.
Water softener systems use a process called ion exchange to remove calcium and magnesium, which are the hallmarks of hard water. Water that is too hard can make household cleaning difficult, as it often leaves residue on kitchen and bathroom fixtures, dulls clothes, and leaves stains on dishes. However, water softening should be used with caution, because it exchanges sodium with the minerals that give the water hardness characteristics, and can be harmful for those who follow a low sodium diet. The sodium produced by water softening can also be harmful to plants. The different types of water softener systems all use ion exchange, but vary in the amount of operator input they require.
Hard water comes from groundwater sources, such as aquifers, because calcium, magnesium and other minerals dissolve in the water from surrounding rocks. Calcium and magnesium cause features that are referred to as hard. Hardness is measured in grains per gallon (GPG), with a grain of hardness equal in weight to a grain of wheat. Any water with more than 1 GPG of calcium and magnesium is considered hard, while more than 10.5 GPG is classified as very hard.
Sometimes chemicals are added to laundry detergent to soften the water used to wash clothes, but all water softening systems that treat the water used by an entire home use ion exchange. An ion is an electrically charged molecule, and different ions can have different charge intensities. Water softeners contain an exchange medium, which is initially coated with positively charged sodium ions. The calcium and magnesium ions in hard water are also positively charged, but they have a stronger charge than the sodium ions. This means that when water passes through the exchange medium, calcium and magnesium ions are captured by the medium, while sodium ions are released from it, because calcium and magnesium ions have a greater attraction.
Eventually, the medium of exchange in a water softening system becomes completely coated in calcium and magnesium ions. When this happens, the water softener is rinsed with a sodium chloride solution, a process known as refilling. The calcium and magnesium ions form compounds with the chlorine and are washed away, while the sodium ions re-attach to the exchange medium.
The different types of water softener systems vary according to the work that the user has to do to recharge them. The most popular type of home water softeners are automatic water softeners, also sometimes called fully automatic water softeners, which use an owner-set timer to automatically recharge the system. Another type of water softener that works automatically is regeneration on demand (DIR), which determines when the system needs to be refilled based on the amount of water used.
Both manual and semi-automatic systems require more user input. A semi-automatic water softener requires the owner to manually tell the softener when to refill. Manual softeners require the user to set all parameters for recharging the softener, including when the system is recharged and for how long.
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