water softener

noun

1. any of a group of substances that when added to water containing calcium and magnesium ions cause the ions to precipitate or change their usual properties: used in the purification of water for the laboratory, and for giving water more efficient sudsing ability with soap.

water softener

noun

1. any substance that lessens the hardness of water, usually by precipitating or absorbing calcium and magnesium ions
2. a tank, apparatus, or chemical plant that is used to filter or treat water to remove chemicals that cause hardness