Hardness of water quality is a property of water resistance and soap bubble. It is an old concept used to describe the content of calcium and magnesium in water. There are different kinds of hardness (total hardness, carbonate hardness and other hardness), and there are different concepts and definitions in different countries.

Hardness salts generally include ca2+, mg2+, fe2+, mn2+, sr2+, te3+, al3+, etc. which are easy to form insoluble metal cations. In general natural water, ca2+, mg2+, and other ions are less. Therefore, the total ca2+, mg2+ in water is usually used as the definition of hardness.

Specifically, the total amount of Ca2 + and Mg2 + is called total hardness. According to the principle of hypothetical compound and considering the composition of anions in water, the hardness can be divided into carbonate hardness and non carbonate hardness.


If the hardness of water is caused by calcium bicarbonate or magnesium bicarbonate, this kind of hardness is called temporary hardness, because it is easy to become precipitation when boiling.

If the hardness of water is caused by sulfate and chloride of calcium and magnesium, it is called non carbonate hardness. This kind of hardness can not be separated from water by general boiling method, so it is also called permanent hardness. Hardness has different concepts and definitions in different countries, but all kinds of hardness refer to the content of CaO or CaCO3 in a certain volume of water.