Reverse osmosis was investigated for purifying Space Station washwater. Experiments were performed on membrane coupons and spiral-wound membrane modules. The membranes were operated at pasteurization temperature (74°C) to prevent microbial growth. Effects of temperature and various surfactants were studied. The permeate quality was determined by analyzing the composition of the water for individual ions, surfactants, and organics. The membrane of choice has acceptable separation performance. An activated carbon post-filter removed residual organics such as surfactants and urea from the membrane permeate. A preprototype washwater reclamation unit was built and operated continuously for 12.5 days, and approximately 2200 gallons of water were processed; this quantity of water would meet the requirements of an eight-person crew for 41 days. The unit operated according to design and processed water meeting the NASA hygiene water processing (separation) standards.