Abstract: A water leak detection and prevention system employs water flow, moisture and temperature sensors within a monitored residential, commercial or industrial building. A motor-actuated valve has been installed that controls water flow through the main water pipe or branch pipe. A flow sensor is used to detect water flow through a building's main or branch water pipe. Moisture sensors and temperature sensors are placed at strategic locations throughout the monitored building. All sensors communicate wirelessly with a gateway. A signal is sent to the gateway whenever a sensor detects a dangerous condition. Signals are relayed from the gateway to a server that manages the system. Alerts are sent to building personnel via push notification and phone calls. Any of such personnel can transmit a command to the server, which is relayed to the affected gateway, which sends a wireless signal to shut off the motor-actuated valve.