Abstract: The invention relates to a reverse-osmosis water desalination plant comprising: a reverse-osmosis membrane unit (TP); at least one high-pressure pump (HP); a pressure-exchange-type energy collector (SRE) capable of transferring pressure from the concentrate leaving the membrane unit to a portion of the water to be treated; sensors for various operating parameters, in particular pressure, flow rate, temperature and salinity level, said sensors being provided at suitable locations; and control loops so that the various adjustable elements are maintained at a setpoint value. The plant also includes a secondary control system (D) comprising calculation means (26) programmed to determine, on the basis of the operating conditions of the plant supplied by the sensors, a combination of setpoint values for the flow rate of the high-pressure pump, the mixing ratio of the energy collector and the conversion ratio, which combination minimizes the energy consumption of the high-pressure pump.