Colorimetry with a mixed indicator
Copper(II) ions can delay or (in higher concentrations) even block the colour change of the indicator. For this reason allow enough water to run through copper pipes prior to sampling.

The total hardness of water is based on its content of alkaline earth ions (calcium and magnesium ions). This content depends on the geological conditions the water encounters during its course and may vary widely. Knowledge of the total hardness is important for the use of water in industrial as well as municipal applications, e. g. in the household as wash water or as boiler feed water in industry.