The water in the Arabic Gulf is known to be challenging for reverse osmosis (RO) seawater desalination. The water is relatively shallow and the temperatures are high. Many small islands off the coast reduce the water exchange with the open sea. This results in seawater with high salinity, high organic content and microbiological activity posing a very high fouling risk for the RO membranes. Carefully designed pretreatment is absolutely essential to ensure economical plant operation.