hard water(redirected from Water hardness)
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Related to Water hardness: water softener
water containing ions, such as Mg2+ and Ca2+, that form insoluble salts with fatty acids so that ordinary soap will not lather in it.
Etymology: AS, heard + waeter
water that contains certain cations, particularly calcium and magnesium, that precipitate with soap solutions. The term is generally applied to tap water, and the degree of hardness varies with the source and previous treatment.
hard waterWater with a high content of calcium and magnesium salts–eg, carbonates and sulfates, which may interfere with certain lab tests. See Mineral water, Spring water; Cf Soft water.
hard wa·ter(hahrd wawtĕr)
That containing ions, such as Mg2+ and Ca2+, which form insoluble salts with fatty acids so that ordinary soap will not lather in it.