The focus of this work is on the operation of a helicon thruster with water as the propellant. The characteristics of a water plasma are investigated and used to develop an analytical thrust efficiency model for the system. The efficiency of a helicon thruster operating with water vapor is compared to the efficiency with traditional noble gas propellants. Next, the predicted efficiency range is compared with other state-of-the-art electric propulsion devices. The addition of an ‘electrodeless’ ion cyclotron heating stage is investigated as a means of increasing thrust efficiency. The thrust efficiency model is extended to assess the parameter space for which the addition of ion cyclotron heating improves performance. Additionally, a particle-based trajectory model is developed to study antenna sizing, phasing effects, and energy conversion. Finally, the effects of second-order reactions on plasma composition and acceleration efficiency are explored using particle balance and particle-in-cell methods.