Abstract: A water feed device for feeding water to a moistener for moistening envelope flaps that is incorporated into a mail handling machine, the water feed device comprising a reserve stock of water from which a quantity of water flows to a reservoir of water with which the reserve stock of water is in communication, said quantity of water being suitable for imbibing a piece of foam soaking in said reservoir of water, said reserve stock of water being disposed in a receptacle that is mounted to move vertically between a low position and a high position, which positions correspond respectively to a low water level and to a high water level in said reservoir, it being possible for the receptacle to take up a plurality of other positions between said low and high positions.