System to controle the volume stored in a tank

The system has a cap (22) whose opening permits introduction of liquid in a tank (1). A detection sensor (21) detects opening/closing of the cap. An electronic module (27) records volume of the liquid stored in the tank between a closing instant and an opening instant. A measuring unit connected to the electronic module measures volume of the liquid. An intermediate chamber (28) is arranged in downstream of the cap. The measuring unit includes a flowmeter (24), which indicates the volume of the liquid passing between the intermediate chamber and the tank. The measuring unit is constituted of a controlling gauge (13) and a pump (25).