Abstract: A reverse osmosis water desalinization system (21) having a reverse osmosis cell (31), a hydraulic pump (34), a motor (39), which is preferably an electric motor and is coupled to drive the pump (34), a conduit array for flow of water through the cell and the rest of the system, and an energy recouperation assembly (22) formed to recover energy from the brine stream from the cell (31) and to input the recovered energy into the pump (34). The energy recouperation assembly (22) preferably includes a fixed displacement hydraulic motor 38 mechanically coupled through a stepless, adjustable ratio increaser assembly to drive pump (34). In a preferred form, the electrical motor (39) is powered by a hybrid photovoltaic/battery bank assembly (42,43) and controlled by a controller (44) which operates the pump (34) only during daylight hours at speed determined by, and with preference given to, the availability of solar power. A water desalinization method also is disclosed.