Abstract: A sensing and dispensing system for dispensing a first liquid to a reservoir, the dispenser comprising a pumping device having an inlet adapted to receive said liquid and an outlet adapted to be placed in communication with the reservoir and a control mechanism controlling operation of the pumping device whereby, in use of the dispenser to effect operation of the pumping device to pump a metered amount of the first liquid into the reservoir. The control circuit may include a sensor for detecting the commencement of delivery of another liquid to the reservoir or a detector for monitoring the conductivity of the liquid in the reservoir.