Glossary

Hardness

Water hardness is a conceptual system of applied chemistry that developed from the needs of using natural water with its dissolved ingredients. Water hardness refers to the equivalent concentration of alkaline earth metal ions dissolved in water, but in special contexts also their anionic partners. The "hardeners" basically include calcium and magnesium ions and normally only traces of strontium and barium ions. The dissolved hardeners can form insoluble compounds, in particular lime and lime soaps. Water is called soft or hard when calcium carbonate concentrations are less than 1.3 millimoles or more than 2.5 millimoles per liter.