Water is an attractive candidate for condensable propellants owing to its availability, handleability, and sustainability. This study proposes the use of water vapor as a propellant for a low-power Hall thruster, and experimentally demonstrates the feasibility of this proposal. Based on the performance estimation from the plume diagnostics, a thrust-to-power ratio of 19 mN/kW, specific impulse of 550β860 s, and anode efficiency of 5β8 % were obtained at an anode power of 233β358 W. From further efficiency analysis, the mass utilization efficiency of water was found to be the most deteriorated among the internal efficiencies compared to the conventional xenon propellant, which was consistent with the expectations from a small discharge current oscillation, large beam divergence, and increase in low-energy ions. Moreover, additional power loss via reactions unique to polyatomic molecules was indicated by evaluation of the ionization cost. In this experiment, the mass utilization efficiency was improved with an increase in the anode voltage from 200 to 240 V without degradation of the power utilization. This suggests that operating at a higher voltage is more suitable for a water-vapor Hall thruster.