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Comment by WiseWeasel | Hacker News Reader

I wonder if that flow rate would be high enough to build this membrane into a drinking straw, so you could take a safe drink right out of the ocean with a cheap, compact device. This seems like it has the potential to revolutionize camping and survival in the near-term, and eventually the availability of clean water everywhere.

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I am far from an expert here, but http://en.wikipedia.org/wiki/Reverse_osmosis#High_pressure_p... and http://urila.tripod.com/desalination.htm/ both claim one needs Over 20 bar of pressure for reverse osmosis. I doubt anyone can suck that hard (apologies for the pun)

The whole point of the article is that this membrane has about 1000x higher flow rate than RO filters.

I still am not an expert, but the way I understand this is that, at say 30 bar, this membrane would produce 1000 times the amount of desalinated water as a conventional system, not that it would produce 100 times more at 3 bar or 10 times more at 0.3 bar than conventional ones at 30 bar.

Actually, we already have that:

http://en.wikipedia.org/wiki/LifeStraw

Interesting, but the linked device doesn't seem to desalinate water. It claims to filter out disease-causing organisms.

Ah, it seems you're right. My mistake.

Wouldn't the water have to be sanitized first? It sounds as if it only filters sodium, not other dangerous particles.

It sounds like it pretty much just lets H2O through, but it's possible that other small molecules could as well. It certainly wouldn't allow for any sort of organism, but harmful elements could get in.

Not much is both water soluble and smaller than sodium. For the most part your basically left things like individual molecules of lead or other heavy metals which you would need to drink a lot of water from vary contaminated sources before you had a problem.

Ed: Individual sodium atoms are smaller than individual lead atoms. However, under the assumption that there is some variation in filtering capability's that will let a low % of things in that are sodium sized and slightly larger through you may have to deal with some larger atoms like lead.

It would have to pass through a fairly hydrophobic (the pore) layer. The water can barely get through since it's polar but uncharged; most metals in solution are charged ions and wouldn't be able to pass through the barrier.

The pore size is very slightly bigger than a single water molecule, and smaller than a single sodium ion. Heavy metal atoms are much larger than sodium atoms, and would not go through the membrane. Any kind of virus or bacteria is much, much larger than this molecular scale, and have no hope of traversing. I am not aware of any harmful water-soluble substances as small as a water molecule.

Hydrogen fluoride comes to mind, but it's probably not an important pollutant in most of the water sources we care about.

I can't think of anything else that small that would be a problem.

Wouldn't hydrogen fluoride just be fluoride ions in solution? Water molecules tend to clump around charged ions, which might impede traversal of the membrane.

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