This is more economic than purchasing the equipment and the resin for ion exchange and paying for the labor and chemicals to operate the process. When a household requires soft water, it is out of the question to operate a small installation for the lime-soda processes. Instead, vendors supply ion exchange resin in tanks, deliver them to the home, and periodically replace them with regenerated resin. An expense that would seem high for a community dealing with large volumes seems not so great for a homeowner with small volumes who is influenced by television advertising. Water may be termed hard because of dissolved salts, but some ions are much more objectionable than others.
Ordinary soap is composed of fatty acids that have insoluble salts with calcium or magnesium ions.
Washing with soap in hard water produces a dingy precipitate that gives clothing the tattle tale grey look. Modern detergents are formulated to minimize precipitation with ions in water, but the feel and cleaning action of hard water are not as good as with soft water. Advertisements by companies that provide water softening service are common. Hardness is expressed in parts per million of dissolved solids. This is almost the same as milligrams per liter.