This work deals with the optimization of energy consumption in a reverse osmosis desalination unit which has a capacity of 30,000 m(3)/day. The studied unit has four double staged lines one of which is equipped with a booster pump (BP). Feed water is pressurized by a high pressure pump (HPP) which brings it from 3.10(5) to 145.10(4) Pa. The results of simulation show that energy consumption in the unit is about 417 kW. This corresponds to a specific consumption of 1.27 kWh/m(3) of osmosed water. It was found that the presence of a BP in the fourth line reduces energy consumption by 21% approximately. The simulation was validated by an exergy analysis which made it possible to evaluate the contribution of the equipments in energy degradation. It showed that the HPP is responsible for roughly 44% of the total exergy loss. The use of a BP has brought this contribution down by 8%. Finally, a technico-economic study was carried out in order to assess the impact of using Pelton turbines and pressure exchangers on the performances of the unit. This study showed that the combination of a pressure exchanger and a BP can lead to a reduction in energy consumption of around 40%. (C) 2010 Elsevier B.V. All rights reserved.