Indicator tablets for determination of water hardness by titration with EDTA.

The tablets are dissolved in 100 ml of the water sample to be tested, which has been buffered at pH 10 with 1 ml of Ammonia/ Ammonium chloride buffer solution, and then titrated with EDTA solution (0,01 M) till the sample turns from red to blue.

Total hardness in mg/l = 10×ml of titrant used.

Control samples of calcium carbonate should be used to calibrate the method.