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Almost. You would have to maintain your underwater base at 1atm and you would indeed get free freshwater. The catch is that the internal volume of your underwater base would decrease and you would eventually have to eject wastewater by pushing against the deep sea pressure. Nothing's free in physics!

But what would take more energy? Pushing that wastewater out or desalinating?

Pressure (N/m^2) times volumetric flow (m^3/s) equals power (N-m/s). At 231 meters the pressure is ~340 psi or ~6.3 MPa. 1 liter would take ~6.3 kJ to pump.

Adding an open window to your suboceanic base sounds like an awful idea, frankly. It's not difficult to see the obvious problem.

Delightfully close to “a screen-door on a submarine”.

Also depends on the energy/materials needed to make and maintain that membrane, I guess.