Which salt cannot cause hardness in the water?

The naturally occurring water and ordinary tap water contain, among other things, dissolved gases (O2, N2, CO2) and a number of salts. These include calcium and magnesium salts, especially their chlorides, sulfates and hydrogen carbonates, which are used as Hardness builders are designated.
Hydrogen carbonates are formed by dissolving calcium carbonate (lime, CaCO3) by reaction with water containing carbon dioxide:
CaCO3 + H2O + CO2 ---> Ca (HCO3)2
Since the hydrogen carbonates are converted into carbonates in the heat, some of the calcium salts precipitate again as poorly soluble calcium carbonate when cooked.
Ca (HCO3)2 ---> CaCO3 + H2O + CO2
If the proportion of magnesium ions in the water is very high, basic magnesium carbonates can also precipitate. This part of the hardness is known today as Carbonate hardness earlier than temporary hardship, since this part can be removed by boiling.
The permanent hardness is caused, however, by the sulfate and chloride ions. Their calcium and magnesium salts cannot be precipitated by boiling.
The total hardness is understood to mean the alkaline earth metal, i.e. the Ca and Mg ions; In general, the total hardness consists of 70-85% Ca and 30-15% Mg hardness.
Soft water has a relatively low concentration of hardness components, hard water a high.