In “Hardness in Drinking-water” report issued by the World Health Organization (WHO) in 2011 mentioned: hardness in 0-60mg/L for soft water, hardness in 60-120mg/L for medium soft water, hardness in 120-180mg/ for hard water, hardness ≥180mg/ for high hardness water; In China, the hardness of drinking water is measured by converting dissolved calcium and magnesium into calcium carbonate, which is measured in each litre of water.
