This paper presents a case study of the operation and maintenance of 2000 m(3)/d desalination plant erected,in 1995. The results have been obtained over 6 years of operation. The plant consists of four units with a capacity 500 m(3)/d each,. The results obtained are used to evaluate and develop the optimum plant operating pressure and temperature. The daily feed salinity, temperature and pressure were recorded, and finally the total cost for product of potable water was calculated. Recommendations were issued regarding the optimum operating conditions and the most pertinent operating problems. A technoeconomical analysis is undertaken in order to evaluate the cost of the water produced and technical reliability,of the technology. The objective is to present field results of the reverse osmoses plant operation in order to evaluate the reliability of this technology in comparison With other technologies.