By means of the application of a pressure exchange system PES, which is already used in other domains, a considerably higher efficiency of energy recovery of reverse osmosis systems may be achieved than with the use of reverse running pumps or turbines. The pressure exchange system is suited, above all, for bigger plants i.e. approx. greater than or equal to 2000 m(3)/d permeate production. It enables a simple, variable adaptation of discharge volume and has, due to its design and the direct pressure transmission of high pressure brine to the feed, an efficiency value of approximately 98%. Therefrom results an economic energy recovery, amortization times for such systems varying between 2 and 4 years depending on the place of operation. In the paper the following are presented and explained: Technical details of the pressure exchange system PES Practical experience with pressure exchange systems in the mining industry with pressures between 40 and 160 bar. cr Concept of the application at RO systems with individual and parallel trains, Economic calculations of the example of a demonstration system Concept and design of a demonstration system for an existing RO plant.