The cistern has a cistern body (10) containing liquid and extending along a reference axis (20). A pumping system pumps the liquid from exterior toward interior of the body. The system has a centrifugal pump (30) for pumping the liquid and a degasser (40) connected to the pump. The degasser decreases quantity of air into the pumped liquid. A venturi (50) creates a depression in the degasser. The venturi is positioned at distance of 1 m above the degasser along direction normal to the axis. A sensor (70) i.e. magneto-inductive sensor, measures the quantity of the pumped liquid.
