Abstract: An irrigation system for controlling the operation of a number of control valves each of which controls the flow of water in a corresponding branch pipe leading from a common supply pipe. The system comprises a pair of control lines which extend along the supply pipe and branch pipes to carry a control signal to operate a control unit which operates a corresponding control valve using a low voltage power supply. The control signal is coded by a data generator according to predetermined conditions and is decoded by each of the control units, the coded signal being received at each control unit, and the specified control unit operating only.