Abstract: A tank (10) for the irrigation of plants in hydroponic cultivation maintains intermittently and automatically the water level in the tank and simultaneously controls the filling opening without mechanical closure. The tank is comprised of elements forming an enclosing container with an annular section. It is divided into three chambers: a storage chamber (12), another chamber open at its upper portion forming a filling channel (14), in connection at its lower portion with the storage chamber, and a third chamber called the filling chamber (16), connected by its upper portion to the storage chamber through an overflow-shoot and, by its lower portion, to the plant container through vertical slots (24). The width of these slots is such that they form a sealing weir due to the surface tension of the water as long as the level is under a predetermined minimum point. The storage chamber and the container are connected through an opening (26) which, due to its arrangement and size, throttles the flow.