Optimal plant operation of brackish water reverse osmosis (BWRO) desalination is studied in this work to reduce specific energy consumption (SEC). A comprehensive first-principles based mathematical model, which explicitly accounts for membrane area and hydraulic permeability, pump characteristic curves, and pressure drops along the RO train, is developed and validated by plant data. A constrained nonlinear optimization is formulated and solved for two RO trains with different service times. It is shown that a 16% reduction in SEC is possible by optimizing operating conditions within the normal operating range of the pump while maintaining the same permeate rate. Results are discussed using dimensionless parameters derived in the author's previous work. Suggestions are made to further reduce SEC in BWRO plant operation. (c) 2012 Elsevier B.V. All rights reserved.