A reverse osmosis water production apparatus for use in a body of water includes a first section defining a buoyancy chamber and an elongate second section connected to the first section and configured to define an elongate chamber which extends downward beneath a waterline in use. The elongate chamber is provided with a plurality of elongate reverse osmosis membrane tubes, each tube containing a reverse osmosis membrane. A longitudinal axis of each reverse osmosis membrane tube is substantially parallel with a longitudinal axis of the elongate chamber and the reverse osmosis membrane tubes are arranged around a passage.