The structure of individual reverse osmosis modules, the configuration of t
he module network, and the operating conditions were optimized for seawater
and brackish water desalination. The system model included simple mathemat
ical equations to predict the performance of the reverse osmosis modules. T
he optimization problem was formulated as a constrained multivariable nonli
near optimization. The objective function was the annual profit for the sys
tem consisting of the profit obtained from the permeate, capital cost for t
he process units, and operating costs associated with energy consumption an
d maintenance. Optimization of several dual-stage reverse osmosis systems w
ere investigated and compared. It was found that optimal network designs ar
e the ones that produce the most permeate. It may, be possible to achieve e
conomic improvements by relining current membrane module designs and their
operating pressures.