Wall hydrants have a square flange that can be mounted flush against an exterior wall of a building or installed into a round or square box to recess the hydrants into a wall. They provide access to water in outdoor areas of a building. Wall hydrants do not have handles for starting or stopping the flow of water through the hydrant's valve. Instead, they come with a key that opens or closes the valve to start or stop the flow of water, which helps prevent unauthorized use of the hydrant.