Question:
There is nothing but air on the other side of the membrane. Itis well known that air is very easily compressible and willtake up almost no space, especially as air dissolves inliquids as easily as carbod dioxide does in Pepsi.

My invention will work and will yield enough drinking waterfor a small yacht. Consider that fact that there are lowpressure reverse osmosis membranes that will function atpressures as low as 500 psi and one need only submerge such apressure vessel about 1200 feet in order to get a system likethis to function.

Answer: Water is not very compressable. It would only take a verysmall volume to squeeze back through the membrane to relievethe pressure most of the way. If there was still too muchpressure to unscrew the cap, one could always modify the capto include a small pet to release the small pressure thatremains before opening the cap to enjoy the contents.

Also, your assumption that the pressure inside the membranewould be 2500 psi is incorrect. Since a high pressure membranedoes not start operating until about 1500 psi there would onlybe a differential pressure of 1000psi.

since air is compressible, the membrane would need to withstand thepressure or, the air would compress until there was no pressuredifferential. A noncompressible liquid such as a water prime wouldallow a pressure differential without collapsing.