1- A substance that is used produce soft water (water with reduced hardness). 2- A device used for the same purpose.
A water softener converts hard water, through ion exchange, into soft water. Soft water is mainly used in closed piping systems, such as heating and air-conditioning systems, to inhibit the formation of scale. Hard water, or simply tap water, is not to be confused with heavy water, which is mainly used in nuclear reactors!
by Farid Yanni June 05, 2006