Devices and methods are provided for sensing and stopping an excessive water-flow condition in a water-using appliance such as a toilet. Such excessive water-flow conditions can occur, for example, when a leak or other malfunction is present in the appliance. The devices measure and monitor the time that elapses after the commencement of water flow to the appliance, and interrupt the water supply when the elapsed time reaches a predetermined value. Alternatively, the devices measure and monitor the cumulative volume of water that flows to the appliance after the commencement of water flow, and interrupt the water supply when the cumulative volume reaches a predetermined value.