Indonesia has many mountains and hills in special location. There are rivers and lakes can be used as energy resource. The energy utilization in Indonesia is dominated by energy derived from fossil. In other hand, water energy potential can be developed as renewable energy resource to generate electricity by using water turbine. Due to the high price of water turbine, it can be substitute by modification of centrifugal blower as water turbine. For this reason, blower as water turbine is needed to be investigated further more using numerical study such as CFD ANSYS Fluent Simulation using CFD (Computational Fluid Dynamics) method with ANSYS Fluent 16.0 software is devided by three parts, namely Preprocessing, Processing and Post-processing. This simulation used four variations of opening valve, such as fully open valve, 34⁄ open valve, 12⁄ open valve and 13⁄ open valve which each opening valve variation has five variation of rotational speed. The results and processing data showed that the opening valves and rotational speeds effect to centrifugal blower as water turbine. The bigger opening valve, the higher power is generated until it reached peak point. The highest of centrifugal blower as turbine. Was produced by fully opening valve and rotational speed of 370 rpm, namely 33,77 watt of power and 0,87 N.m of torque. The optimum power had 4,84 kg/s mass flow rate and it efficiency reached 23,69 %.