VPE 511: Environment and Environmental Hygiene (2+1)

HARDNESS

• The hardness of water refers to its soap-destroying power and is due to the presence of calcium and magnesium salts in solution.
• It is usual to distinguish between waters that are “temporary” hard and those that are “permanently” hard .
• Temporary hardness is due to the presence of the bicarbonates of calcium and magnesium in solution, permanent hardness is due to the chloride, sulphates and, to a lesser extent, the nitrates of calcium and magnesium.
• Hardness, whether temporary or permanent, is expressed as parts of calcium carbonate per 100,000 parts of water; “degrees ‘’of hardness are numerically equal to parts of calcium carbonate per 100,000 parts of water.
• A total hardness of more than 30 is sufficient to render a water unsuitable for most purposes , although if required for drinking only a considerably higher hardness might be tolerated.
• Waters with hardness less than 5 are very soft, and such hardness values should be considered along with pH value for possible plumbo-solvent action.