Frost-free yard hydrants are water outlets that are installed in the yard or street to provide free-flowing water throughout the year, even during winter. To keep the water from freezing, the hydrant has a stop-and-drain valve that's located below the frost level about three meters below the ground surface.
When the hydrant is open, water flows through the valve and the riser pipe, then out of the faucet. Closing the hydrant closes the valve and stops the water supply. At the same time the drain hole opens, so that the water in the riser pipe flows through it and out to a gravel bed. During winter, because the riser pipe is empty, no ice formation occurs that can block the pipe.