A separation process of the reverse osmosis type useful for generating fresh water by forcing salt water against a semipermeable membrance that allows only pure water to pass, which uses centrifugal forces created by rotating basket to build up a pressure head of water supplied to the basket to force water through the membrance. The pure water can be expelled by a nozzle in a direction to help rotate the basket. The membrance can be in the form of a spiral or layers extending perpendicular to the axis, to increase the membrane area within a basket of given size. The membranes can extend radially with respect to the axis of rotation, and supply and removal conduits can be positioned to continually flow water in an outward radial direction to prevent the build-up of polarization layers on the membrane surfaces.