Hard water
- Slovak term: Slovenský termín
- Generally, water that requires considerable amounts of soap to produce a foam or lather and that also procudes scal in hot water pipes, heaters, boilers and other units in which the temperature of water is increased materially (Symons et al, 2000).
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See hardness, total.
Explanation
Hardness in water is caused by dissolved calcium and, to a lesser extent, magnesium. It is expressed as the equivalent quantity of calcium carbonate. Hardness above about 200 mg/litre can result in scale deposition, particularly on heating. No health-based guideline value is proposed for hardness (WHO 2004).
Example
With respect to hardness, waters have been classified as follows: 0-25 milligrams per litre as calcium carbonate (CaCO3) as very soft; 25-75 milligrams per litre as calcium carbonate (CaCO3) as soft; 75-150 milligrams per litre as calcium carbonate (CaCO3) as moderately hard; 150-300 milligrams per litre as calcium carbonate (CaCO3) as hard; and 300 milligrams per litre as calcium carbonate (CaCO3) and up as very hard (Symons et al, 2000).
References
- WHO (2004) Guidelines for Drinking-water Quality
- Symons, JM, Bradley LC and Cleveland TC (2000). The drinking water dictionary. American Water Works Association.
