Hardness is not a specific constituent of water. It is due primarily to the presence of ions of calcium and magnesium in water. Hardness is expressed in terms of calcium carbonate (CaCO3). Water with less than 75 milligrams per litre (mg/l) is considered soft, 76-150 mg/l moderately hard, and above 150 mg/l, hard water.
Ion exchange device.
The most common form of water softening is through ion exchange. The video below from Kinetico demonstrates the process:
Non-chemical softeners. Some manufacturers claim their devices instead of exchanging ions, the minerals in the water are crystallized so that they do not bind to surfaces. The main benefit to the user is the elimination of the need to deal with adding salt to the system.
Negative Effects of Hard Water:
There are no known health risks associated with the consumption of hard water. In fact, studies have shown that people who regularly consume hard water throughout their lifetime have a lower rate of cardiovascular disease.There are some problems associated with hard water. These include grey staining of washed clothes, scum on wash and bath water following use of soap or detergent, reduced lathering of soaps, buildup of scale on electric heating elements and boilers, reduced water flow in hot water distribution pipes due to scale buildup, accumulation of whitish-grey scale in tea kettles and other containers used to boil water