Abstract: An apparatus for automatically controlling the flow of fluid in an inlet conduit that provides the water supply for a home or building so as to prevent water damage due to a failure in the water system when unattended. The apparatus comprises a power circuit for supplying a low voltage DC power output which is connectable to a standard AC power source and includes an internal battery which operates in case of AC power failure. A flow sensor and a shutoff valve are connected in the inlet conduit. A control circuit which can be preset for different operational modes, receives and processes flow status signals from the flow sensor and provides output signals that control the shutoff valve, so that if continuous flow is detected in the conduit for a time period exceeding a preselected time, the shutoff valve will automatically close.