Hardness
Archaeometallurgy, Guidelines for Best Practice, published by Historic England in 2015, defines hardness as: ‘…a measurement of the strength of a material (its ability to resist plastic deformation).’
The word 'hardness' may also be used to refer to water that contains a high amount of dissolved calcium and magnesium. Hard water is found in areas which have a chalk and limestone geology. Soft water has a low level of calcium and magnesium compounds.
Water safety in buildings, published by the World Health Organization in 2011, states:
- ‘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, 2008).’
- ‘Hardness is caused mainly by the presence of calcium and magnesium in the water. Scale formation and excessive soap consumption are the main concerns. When heated, hard waters have a tendency to form scale deposits, which shorten the life of water heaters and other appliances (Health Canada, 2009).’
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