A water treatment sensor includes a housing having a bottom with an exterior surface in contact with a flow path of a fluid and an interior surface. First and second probes spaced from one another extend from the exterior surface and into the flow path. A first circuit electrically connects the first and second probes and determines a conductivity from a measured resistivity between the probes. First and second temperature sensors are spaced from one another and are coupled to the interior surface. The first sensor determines a temperature of the fluid. A temperature elevated by a heat source and determined by the second sensor is maintained above the temperature of the fluid. A second circuit determines a flow rate of the fluid based on adjustments to the heat source. Communication circuitry communicates the conductivity, the temperature, and the flow rate of the fluid to a controller.