Powerful micropumps and water sterilization are essential for biomedical applications using microfluidic circuits. Therefore, we propose a rotary pump using underwater electrical discharge for water sterilization and elucidate its design concept. Specifically, we demonstrate that by applying high-voltage pulses repeatedly, the rotary device having an asymmetrical antenna structure can rotate with the maximum angular velocity of ~25 rad/s, and can produce a net flow with an average velocity of $\sim$3.2 mm/s along with an instantaneous maximum flow of ~9 mm/s. In addition, we explain our experimental results fairly well by proposing a simple model that considers the effects of asymmetricity and electric field strength with a steric effect. Our findings should contribute to the microfluidics for biomedical applications.