Abstract: A monitoring apparatus for carrying out the method is connectable by a telephone line to a central computer system. The apparatus includes first and second input ports for receiving first and second signals, respectively. The first signal represents a volumetric water flow rate while the second signal represents a physical characteristic of the treated water. A processing circuit is connected to the input ports and includes a microprocessor programmable for receiving and totalizing the first signals to a flow volume. The processing circuit also includes a real time clock connected to the microprocessor for continuously computing time. A power supply provides the necessary voltages to the apparatus.The apparatus is arranged to initiate a call to the central computer system upon the occurrence of any one of two or more described conditions such as measured deterioration of water quality, lapse of time or others. Several embodiments are disclosed.