Deep sea pressures ( minimum 27 bar or 270 m deep ) were utilized to produce fresh ( not salty ) water bu using the existing membrane system . Theoretically the pump pressure ( required energy ) to put into a steady flow operation is near to 27 bar or over head pressure of the sea water.

Using a specially designed pressurized tank , the concept was verified experimentally.

Details can be found in patent / publication # 20140339169

LARGE VOLUME SUB-SEA WATER DESALINATION REVERSE OSMOSIS SYSTEM, METHODS, AND APPARATUS

Abstract: A reverse osmosis sub-sea desalination system is disclosed. The reverse osmosis system may include a reverse osmosis station configured to generate fresh water from salty water, a storage tank configured to store fresh water downstream of the reverse osmosis station, and a pump fluidly connected to the reverse osmosis station and the storage tank. The reverse osmosis station, the storage tank, and the pump may be disposed at one or more depths beneath a surface of a body of salty water.