A water conductivity monitoring circuit determines the status of an ion exchange filter in the water flow to a steam generator. A microprocessor sends a reference signal to a conductivity sensor circuit that converts it to an excite signal that is sent to a probe in the water flow. Any conductivity of the water alters the excite signal, and the modified signal is compared to the reference signal to establish a value indicative of the conductivity of the water. The microprocessor compares the value to at least two thresholds representative of the status of the filter.