Desalination system includes a submersible module defining a water-receiving interior and including openings leading from the interior to an exterior, reverse osmosis (RO) membranes arranged in each opening such that the RO membrane is exposed to seawater when the module is submersed, a pump arranged in connection with the interior of module, and a movement system for adjusting the vertical depth at which the module is submersed. The movement system can move the module in vertical and horizontal directions, in any predetermined pattern, or in vertical--horizontal planes defined by the movement system from one location to another location to prevent an elevated salt concentration in an area adjacent the RO membranes and to thereby maintain the osmotic pressure of the seawater in the area adjacent the RO membranes low.