In order to optimise brackish water desalination, Vitens and DHV have developed a hydraulic optimised pressure vessel (Optiflux((R))), which reduces the pressure loss significantly and thereby increases the productivity of the membranes by 15-20%. The Optiflux((R)) concept is applied full scale in the Vitens water treatment plant Engelse Werk at Zwolle, The Netherlands. The plant is currently under construction and the production of drinking water is expected to start in the first half of 2003. Currently, seawater desalination plants tend to operate at a higher flux and possibly at a lower recovery (due to the introduction of energy recovery from the concentrate flow), which will lead to a higher flow per pressure vessel, resulting in higher hydraulic losses. These developments will result in an increasing potential for the application of Optiflux((R)) in seawater desalination plants. Based on current practice as well as the expected developments in desalination the authors believe that the full scale implementation of Optiflux((R)) will have significant spin off in future brackish and seawater desalination plants.