Test strips Aquadur®

Determination of Water Hardness

Water contains a whole host of salts and other compounds in addition to the gases dissolved in it (oxygen, nitrogen, carbon dioxide). Its most important constituents are magnesium and calcium in the form of their chlorides, sulphates and bicarbonates. These dissolved salts are known as hardeners. The bicarbonates precipitate in the heat (during boiling) as carbonates and are known as carbonate hardness or temporary hardness. The sulphate and chloride compounds are known as permanent hardness or non-carbonate hardness. Total hardness describes the concentration of alkaline earth metal ions in water.

The unit of measurement for water hardness used to be 1 °dH (German degrees of hardness), which corresponds to 10,00 mg CaO or 7,19 mg MgO in one litre of water. Today we use millimoles per litre (mmol/l), whereby 1 °dH corresponds to 0,18 mmol/l of earth metal ions and 1 mmol/l corresponds to 5,6 °dH.