Abstract: A hydraulically actuated shut-off valve is controlled by a solenoid actuated control valve. A flow detection unit having a substantially vertical inlet and a substantially vertical flow passage has a substantially horizontal outlet connected to the horizontal inlet of the shut-off valve. A member movable by water flowing through the flow passage actuates a switch forming a part of the flow detection unit. A control box preferably mounted on the flow detection unit has a timer and a reset switch therein which are capable of sending electrical control signals to the solenoid actuator of the control valve. The timer senses the condition of the flow detection switch and upon sensing that the switch has been closed a predetermined period of time suggesting abnormal water flow, possibly due to a leak in the system, sends a signal to the solenoid to actuate the control valve to cause the shut-off valve to close, preventing further water flow.