A reverse-osmosis water desalination plant comprising: - a reverse-osmosis membrane unit, - at least one high-pressure pump for taking a first portion of the water to be treated to a pressure higher than its osmotic pressure and sending it to the inlet of the membrane unit, - a means for adjusting the flow rate of the high-pressure pump, this means comprising an adjustable valve installed on the outlet of the high-pressure pump and/or a drive motor for driving the pump at variable speed, - an energy collector of the pressure-exchange type suitable for transferring the pressure of the concentrate leaving the membrane unit to a second portion of the water to be treated, this collector comprising - a first inlet receiving the second portion of the water to be treated, - a second inlet receiving the concentrate, - a first outlet delivering to an inlet of the membrane unit a mixture between a first portion of the concentrate and the second portion of the water to be treated, - a second outlet delivering a second portion of the concentrate, and - a means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water-to-be-treated, and - an adjustable control valve installed at the second outlet of the collector, making it possible to adjust the conversion rate, - sensors of various operating parameters, in particular pressure, flow rate, temperature, salinity ratio, provided in appropriate locations, - control loops so that the means for adjusting the flow rate of the high-pressure pump, the means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water to be treated, and the adjustable control valve are maintained at a setpoint value, - a secondary adjustment comprising computing means programmed to determine, based on 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 mixture ratio of the energy collector, - and the conversion ratio, which makes it possible to minimize the energy consumption of the plant, these setpoint values being situated within limits ensuring the quantities and qualities of water produced and the behavior of the equipment, - and means of connection between, on the one hand, the outlets of the secondary adjustment and, on the other hand, the means for adjusting the flow rate of the high-pressure pump, the means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water-to-be-treated, and the adjustable control valve, in order to insert therein these setpoint values. - a reverse-osmosis membrane unit, - at least one high-pressure pump for taking a first portion of the water to be treated to a pressure higher than its osmotic pressure and sending it to the inlet of the membrane unit, - a means for adjusting the flow rate of the high-pressure pump, this means comprising an adjustable valve installed on the outlet of the high-pressure pump and/or a drive motor for driving the pump at variable speed, - an energy collector of the pressure-exchange type suitable for transferring the pressure of the concentrate leaving the membrane unit to a second portion of the water to be treated, this collector comprising - a first inlet receiving the second portion of the water to be treated, - a second inlet receiving the concentrate, - a first outlet delivering to an inlet of the membrane unit a mixture between a first portion of the concentrate and the second portion of the water to be treated, - a second outlet delivering a second portion of the concentrate, and - a means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water-to-be-treated, and - an adjustable control valve installed at the second outlet of the collector, making it possible to adjust the conversion rate, - sensors of various operating parameters, in particular pressure, flow rate, temperature, salinity ratio, provided in appropriate locations, - control loops so that the means for adjusting the flow rate of the high-pressure pump, the means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water to be treated, and the adjustable control valve are maintained at a setpoint value, - a secondary adjustment comprising computing means programmed to determine, based on 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 mixture ratio of the energy collector, - and the conversion ratio, which makes it possible to minimize the energy consumption of the plant, these setpoint values being situated within limits ensuring the quantities and qualities of water produced and the behavior of the equipment, - and means of connection between, on the one hand, the outlets of the secondary adjustment and, on the other hand, the means for adjusting the flow rate of the high-pressure pump, the means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water-to-be-treated, and the adjustable control valve, in order to insert therein these setpoint values. - and means of connection between, on the one hand, the outlets of the secondary adjustment and, on the other hand, the means for adjusting the flow rate of the high-pressure pump, the means for adjusting the mixture ratio between the first portion of the concentrate and the second portion of the water-to-be-treated, and the adjustable control valve, in order to insert therein these setpoint values.