Water hardness is divided into carbonate hardness and the non-carbonate hardness.

Carbonate hardness

It is mainly composed of calcium and magnesium bicarbonate [Ca (HCO3) 2, Mg (HCO3 formed) 2], and a small number of carbonate hardness. The heat decomposed bicarbonate hardness to remove sediment from water, sometimes referred as temporary hardness, the reaction is as following:

The non-carbonate hardness

It is mainly composed by calcium and magnesium sulfate, chloride and nitrate salts. Such hardness can not be removed by heat decomposition, it is also known as permanent hardness, such as CaSO4, MgSO4, CaCl2, MgCl2, Ca (NO3) 2, Mg (NO3) 2 and so on.

Carbonate hardness and non-carbonate hardness is called total hardness.

Content of Ca2 + in water is called calcium hardness.

Content of Mg2+ in water is called magnesium hardness.

When the total water hardness is less than the total alkalinity, their difference is called the negative stiffness. Watercolor is natural water or treated water colors of various indicators when the quantitative determination of reverse osmosis scales inhibitor. Watercolor often affects the quality of paper, textile and other industrial product. Various uses of water have certain requirements for color: the color of domestic water is less than 15. ; Paper industrial water is less than 15-30. ; Textile industrial water is less than 10 - 12. ; Dyed water is less than 5 phosphate crystal silicon.

Industrial wastewater may produce a variety of colors, but the humus holds water, suspended sediment and dissolved minerals also can make the water with a color. For example, clay makes the water with yellow, iron oxides make water become brown, sulfide makes water become light blue, algae makes the water green, corrupted organic compounds make water black-brown, etc.