hard water

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hard wa·ter

water containing ions, such as Mg2+ and Ca2+, that form insoluble salts with fatty acids so that ordinary soap will not lather in it.

hard water

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.
Water with a high content of calcium and magnesium salts—e.g., carbonates and sulphates—which may interfere with certain lab tests

hard water

Water 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.
References in periodicals archive ?
This first hardness scale was still very unreliable because the testing implements themselves (file, knife and fingernail) were not standardized and could vary in hardness.
While he was still curator at the Johanneum in Graz, Austria, he refined Hauy's hardness scale, eliminating glass from its illogical place in the system.
In his Versuch einer Elementar-Methode zur naturhistorischen Bestimmung und Erkennung der Fossilien (1812), Mohs first introduced the ten-step hardness scale that is still in use today: