it's always an issue of volume flow and membrane effectivenes with these things. many things 'work' that don't work to resupply the population on a daily basis.

Nanoporous graphene is pretty awesome stuff. The numbers are up in the range of 4 litres per square centimetre per hour per megapascal. Or more practically, just a one centimetre by one centimetre "hole" at the bottom of a 100m tall "tank" (it can actually just be a pipe, the key is the water depth not the reservoir capacity) would produce 4 litres per hour powered by nothing but gravity. Of course there's the requisite effort of approximately 100N of work per litre to lift it up that hundred meters, but being otherwise passive is a good illustration of how much more efficient these materials are.

Yes I know I'm ignoring things like biofilm buildup, particulate settling, etc. I'm mainly trying to illustrate the "basic work" required to get drinking water from sea water using the latest technology. Most existing reverse osmosis membranes are only capable of 1 litre per square centimetre per megapascal per DAY. That's not even a remotely practical rate without mechanically applied pressures, and since we're now dealing with hydraulic pressures... a lot more engineering and maintenance.

Thank you, was going to mention the flow rate vs current reverse osmosis tech.

I am still wondering about the efficiency in terms of filtering toxins. Water molecules are smaller than most other molecules but I am not sure if some toxins would still be able to get through the holes in the graphene? Things like heavy metals