In this paper, an industrial medium-scale brackish water reverse osmosis plant based on Dow/FilmTec BW30-400 spiral-wound membrane modules was simulated and its performance investigated. Actual operating data is used to validate the computer package. The semi-rigorous model was found to represent the plant with good accuracy; the relative errors in the overall water recovery and salt rejection were 0.37 and 1.33%, respectively. The effects of the arrangement of membrane modules, the operating pressure and the feed flow rate on the performance of the plant were investigated. The single-stage configuration in which all pressure vessels are arranged in parallel was found to yield the best results in terms of the production rate, product quality and overall pressure drop across the feed channel. At low to moderate operating pressures and feed rates, increasing both operating variables will result in higher water production rates and salt rejection. However, high operating pressures lead to a deterioration of the quality of the product whereas high flow feed rates, contrary to one's expectation, result in a reduction in the production rate. (c) 2005 Elsevier B.V. All rights reserved.