A controller (8) for a pilot valve (102) which adjusts the output pressure of a pressure reducing valve (44) supplying water to a consumer region (3). With the aim of reducing output pressure whilst still providing a minimum required pressure at a critical point (CP) in the region, the controller adjusts the output pressure in accordance with the flow rate. The controller includes a clock (22) and the relationship between the required output pressure and the measured flow rate is time dependent. Parameters which define the relationship are supplied to the controller (8) from a remote data processing system (13) which analyses flow rate and output pressure data transmitted from the controller, and also pressure data from a remote sensor (10) at the critical point. At intervals, the controller (8) establishes a wireless connection with the remote system (13), to transmit logged data, and to receive parameters covering a period of time which is greater than the interval between communication sessions.