The Basrah University reverse osmosis plant (BURO) is an experimental unit built to provide college laboratories with desalted water. The plant has a total capacity of 9 m(3)/h and is composed of three independent lines. The aim of this study is to develop a theoretical model to predict the performance of reverse osmosis (RO) systems and to compare the theoretical results with experimental values obtained from the pilot plant. The study was conducted using two types of membranes, viz. Saehane, type RE8040BE of South Korean origin and TFC-Koch system membranes model 8822XR of American origin to test the theoretical model that is predicted based on the generalized transport equation system involving solvent (water) and any number of ions (solute) that is dissolved in water using the Kimura-Sourirajan analysis. The main objective of this work can be specified in three steps as follows: (1) develop a computer program as a general model for any type of RO system, (2) predict plant performance as a function of time (8 months of operation), and (3) perform comparative studies on the performance of the two types of membranes specified. The recovery of Saehane membranes is larger than Koch membranes due to the difference in the effective area for both types of membranes whereas the salt passage of Koch was always lower than Saehane membranes for brackish water having TDS larger than 550 ppm. There is agreement between theoretical and experimental results.