The Abu Dhabi solar desalination plant started operation in September 1984 and is still operating until now. The plant was designed as a pilot unit for the evaluation of the technical economic feasibility of such plants for supplying fresh water to remote arid coastal areas of the UAE. The aim was to evaluate the long-term system performance and reliability and determine the optimal operating strategy and maintenance schedule. The plant consists of three subsystems: the solar collector field, the heat accumulator and the seawater evaporator. The solar collector field and the heat accumulator has experienced only a small amount of performance degradation, however, the evaporator have suffered from about 25 percent degradation in performance and is currently in need of an acid and demister cleanings to bring its performance to its original level.