Water softener salt is a coarse grade of salt used in water treatment plants. The large grain size allows for excellent flow through the salt bed. It reduces the calcium or magnesium ion concentration in hard water. These hardness ions cause three major kinds of problems. The metal ions react with soaps and calcium sensitive detergents, hindering their ability to lather properly and forming an unsightly precipitate- the familiar scum or bathtub ring. Presence of hardness ions also inhibits the cleaning effect of detergent formulations. Water softeners are typically used when water is supplied from wells. Public water systems are also susceptible to hard water, although this is much less common.