The aim of this paper is to determine the recovery rate and other performance parameters using a numerical model. The results are presented for a two-stage seawater reverse osmosis desalination unit with spiral-wound modules. The model, which is based on the mass and momentum transport equations, takes into consideration the longitudinal variation of the velocity, the pressure and the salt concentration in the membrane modules. Data given by plant authorities reveal that the plant is currently operating at a recovery rate of 67.53%. This project has shown that for the Desalination Company of Trinidad and Tobago, the recovery rate currently achieved by the plant (67.53%) might not be the most economical. Slightly reducing the recovery rate drastically reduces the energy cost, resulting in an overall reduced cost per cubic meter of desalinated drinking water.