Significant parts of the world are experiencing a continuous unprecedented growth in population, in the standards of life and in industrial development. These factors increase the consumption of water which supply is already under stress. The World Bank has indicated in its Water Management Strategy (Le Moigne et al., 1994) that the water situation in the Middle East is precarious. The renewable water resources per capita have seen a reduction from about 3599 m(3) to less than 700 m(3). Thus, water must now be considered as a limited resource. Under these circumstances, the already scarce sources for ＇＇good＇＇ raw water are becoming less available and raw waters of fewer quality have to be considered as candidates for treatment, including desalination. From the point of view of reverse osmosis desalination, this means that new technological advances are necessary for both, the pretreatment of such waters with high fouling potential to make them adequate for the RO process, and the RO membrane technology itself to produce membranes which are less prone to failure when subjected to pretreated feeds of lower quality. In the following, the improvements achieved by the new FILMTEC** products as well as results of field experiences made with FILMTEC** seawater and brackish water reverse osmosis membranes are presented along with the analysis of the relation between the achieved performance and the pretreatment used in the respective plants. Possible pretreatment steps are analyzed in relation to measured efficiency to Limit the fouling incidence and possible optimization is reviewed as well.