A volumetric meter is the device fitted into a closed conduit, which consists of chambers of known volume and a mechanism driven by the flow, whereby these chambers are successively filled with water and then emptied. The water to be measured enters the inlet of the body and its pressure sets the piston into rotation. Every rotational cycle of the piston discharge a fixed volume of water to the meter of body. The number of rotation of the piston is totalized through a reduction gear, to totalize in the register, when the total volume of water is registered.