The conventional Savonius turbine is one of the most used rotors to convert the kinetic energy of natural water resources instead of potential energy. However, this rotor presents low efficiency. A twisted Savonius turbine was appeared which is considered most performant by twisting the blades of the conventional Savonius turbine along theirs spans. In fact, various experimental and numerical investigations were carried out to enhance the efficiency of the twisted Savonius turbine which has not been completely explored. In this study, an experimental investigation was carried out to assess the performance characteristics of a twisted Savonius turbine in an irrigation canal. In order to improve the efficiency of the Savonius turbine, three deflector designs were investigated numerically based on a CFD 3D numerical model. The peak value of the turbine power coefficient reaches 0.166 at a tip-speed ratio value of 0.78 without using a deflector upstream the turbine. Using the deflector design showing the highest efficiency, the peak value of the power coefficient was increased by 17.47%. The use of the proposed deflector is expected to provide toward a more effective employment of flowing water like tidal currents, river streams or other man-made water channels for electrical energy production in rural regions.