This research work assesses the performance of reverse osmosis (RO) plants in the Arabian Gulf region by analyzing its failure behavior and downtime patterns. The data collected are from an experimental RO plant in the region; these data cover a 4-year operation of the plant regarding the failures of several components and subsystems of the plant. Since the plant was designed for continuous operation, assessment of the availability of the plant was considered to be more appropriate than that of reliability. For the purpose of assessing availability, the plant was divided into four subsystems: beachwell pumps, pre-treatment; RO, and post-treatment. Subjective assessment of failure probabilities of subsystems was made wherever detailed data were not available. The overall unavailability of the RO plant was 0.95 d/y.