For automatic determination, monitoring and LC display of the total residual hardness (water hardness) in the water. The parameter to be measured and the appropriate measuring range are determined by indicator selection and by an appropriate user program. Control via alarm horn, stop solenoid valve or similar devices. Connection provided for recorder and central control station for transmission of analysis results (0/4 - 20 mA output signal), power supply 230 V, 50 Hz with EC type certificate according to guideline 97/23/EC.