Abstract: A water purity testing system includes a sensor housing having an internal chamber within which pair of electrodes are supported. Fittings are provided for coupling the housing to a water supply and introducing water into the chamber. A temperature sensor is supported within the housing. A system processor and control unit is operatively coupled to the electrodes and the temperature sensor and includes a source of voltage DC current measurement which is applied to the electrodes to facilitate the measurement of water conductivity within the housing chamber, followed by a grounding period to provide as settling time to prevent the build-up of debris on the electrodes. The microprocessor also utilizes the temperature measurement during the testing cycle to derive a temperature factored measurement of total dissolved solids within the water under test. A display system is coupled to the microprocessor and is operated under microprocessor control to provide a test result display output.