Energy recovery systems based on turbines activated by concentrate leaving the plant have been in operation in many reverse osmosis (RO) plants for many years. Other design approaches for RO plants save energy by reducing the energy demand for the desalination process itself. One of them is the pressure-exchange system (PES) which is able to achieve considerably lower energy requirements in comparison to the conventional systems, The PES is suited for plants with a permeate production of more than 2000 m(3)/d. It enables a simple, variable adaptation of discharge volume and has, due to its design and direct transmission of high pressure from the brine to the feed, an efficiency of approximately 98%, with economic energy utilization and short amortization times. This proven system has ben used in the field of mining for more than 20 years, and with volume flows of up to 1400 m(3)/h and pressures of up to 16 MPa. On one of the Canary islands, a PES is presently under construction in a RO plant for seawater desalination with a permeate capacity of 5000 m(3)/d for demonstration purposes.