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).
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.
