Abstract: A modular water supply shut off and by pass system that can be installed in a standard water supply line and used to prevent water flow through the supply line except when the system is activated. The system includes a modular unit having main fluid flow line provided with a remotely actuated valve and a by pass fluid flow line provided with a manually operated valve. The system also has a control unit that includes a timing mechanism that be operated to actuate the remotely actuated valve and allow water to flow through the main fluid flow line for a period of time determined by the timing mechanism. A momentary switch is coupled to the control unit and used to actuate the timing mechanism.