This work focuses on the design and implementation of an optimization-based control system on an experimental reverse osmosis (RO) membrane water desalination process in order to facilitate system operation at energy optimal conditions. A nonlinear model for the RO process is derived using first principles and the model parameters are computed from experimental data. This model is combined with appropriate equations for reverse osmosis system energy analysis to form the basis for the design of a nonlinear optimization-based control system. The proposed control system is implemented on UCLA's experimental RO desalination system and its energy optimization capabilities are evaluated. (C) 2010 Elsevier Ltd. All rights reserved.