Abstract: A liquid conductivity monitoring device includes an elongated cylindrical housing having parallel-spaced electrodes at one end for insertion into a liquid carrying conduit, and a transparent user-viewable lens at its other end. The electrodes are connected within the housing to a differential amplifier which provides a change in output signal level when the liquid conductivity exceeds a predetermined threshold level. A pair of oppositely-poled LED's of different colors connected between respective unidirectional current sources and the output of the differential amplifier and viewable through the lens indicate acceptable and unacceptable conductivity levels to the user.