Magnetorheological fluids (MRFs) appear particularly functional for automatic clutch applications due to their capability of rapidly increasing their shear strength when subjected to a magnetic field, and being a viscous fluids when the magnetic field is turned off. They have been investigated since the late 1940s and are employed in different operating modes: in particular, the shear mode is adopted in clutches and brakes. In addition to the controllable property, they have the advantage, with respect to conventional clutches, of not requiring axial loading and the absence of wear. The activity described in this paper has been carried out in the framework of a funded project aimed at evaluating the feasibility of a controllable water pump based on an integrated MRF clutch. The advantages consist of an improvement of the overall vehicle performance and efficiency, in the possibility of disengaging the water pump when its action is not required, and in the control of the cooling fluid temperature. So, the design constraints have been defined with reference to the available space, required torque, and electrical power. After an iterative procedure, in which both mechanical design and magnetic field analyses have been considered, the most promising solution has been defined and a first physical prototype has been realized and tested. A preliminary experimental characterization of the developed prototype has been presented.