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The hardness of a water supply is determined by the content of calcium and magnesium salts. Calcium and magnesium can combine with bicarbonates, sulfates, chlorides, and nitrates to precipitate as solids Mineral salts make water more basic and corrosion aggressive on many materials. The presence of salts in lime scale deposits is one of the most common cause of corrosion, which cause damages in water pipelines and boilers.Any descriptive or numerical classification of hardness of water is rather arbitrary. A water that is termed hard in some areas may be considered soft in other areas. The U.S. Geological Survey uses the following classification:
Soft: less than 60 ppm (as calcium carbonate)
Moderately hard: 60-120 ppm
Hard: 120-180 ppm
Very hard: above 180 ppm
