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The WQA Glossary of Terms
This Glossary is published by the Water Quality Association (WQA) as a service to members and leaders in education, government, and industry.
© Copyright 2010 by Water Quality Association
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H
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Hardness
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Wednesday,Aug 25, 1999
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A common quality of water which contains dissolved compounds of calcium and magnesium and, sometimes, other divalent and trivalent metallic elements. The term hardness was originally applied to waters that were hard to wash in, referring to the soap wasting properties of hard water. Hardness prevents soap from lathering by causing the development of an insoluble curdy precipitate in the water; hardness typically causes the buildup of hardness scale (such as seen in cooking pans). Dissolved calcium and magnesium salts are primarily responsible for most scaling in pipes and water heaters and cause numerous problems in laundry, kitchen, and bath. Hardness is usually expressed in grains per gallon (or ppm) as calcium carbonate equivalent.
The degree of hardness standard as established by the American Society of Agricultural Engineers (S-339) and the Water Quality Association (WQA) is:
Term grains/gallon mg/Liter(ppm) Soft = less than 1.0 less than 17.1 Slightly Hard = 1.0 to 3.5 17.1 to 60 Moderately Hard = 3.5 to 7.0 60 to 120 Hard = 7.0 to 10.5 120 to 180 Very Hard = 10.5 and above 180 and above
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