Steam is the exact opposite of what you need. If your tree was somehow naturally cooler, water from the air would condense directly onto its surface, creating the same effect.

Well, I had a bit of an idea here, actually.

Perhaps it's a steam engine in the sense that at the bottom of the trunk of your 'tree' is some kind of heat-absorbing engine that actively steals heat from the 'leaves' at the top, artificially cooling them. The cool leaves condense water from the atmosphere, and carries it to a holding tank at the bottom, where the heat is reapplied to it, creating a steam engine that would ordinarily power other devices.

In a survival situation, the holding tank can be disconnected from the heat absorber if you want to drink the water, in which case this thing would just be blowing hot air out the bottom.

Riffing off ProximaC, check out Sterling Engines. They would work off the temperature difference above and below the canopy and give you mechanical movement, whether that's a water pump or whatever.

Those things already exist, they are called Atmospheric Water Generators. Which in turn are nothing but Dehumidifiers + filters.
They make water out of air.

http://en.wikipedia.org/wiki/Atmosph...ater_generator

Out of that, the diagram of interest is this one:



Now, out of this some of the most fancy components like the "Electrostatic Air Filter", "Ozone Generator", and "Water Filters" are actually irrelevant to the water extraction process. They simply clean the water from dust, bacteria etc. Since this a steampunk setting and everyone is breathing tons of soot daily anyway and going to die by 30 from this, I assume that this is not a problem.

What remains then, does not *really* require electricity. All the rest are nothing more than fancy pipes through which a "refrigerant" circulates (perhaps the modern creation of it in the factory is complex, but you can handwave it as being done with chemistry), and big mechanical things like pumps, fans etc. A fan is a fan, a steam engine connected to it with belts and such could equally turn one. A compressor is just a fancy pump, ditto. And so on. So basically there is no reason you just can't have a big boxes with grills and a steam engine next to it and say that this makes water out air.

Damn, I wish I would have studied engineering...

I am so sad that I didn't get here fast enough to make Dune jokes.

Yay, I knew someone would come through for me. =] Unfortunately, I've already turned in the model, so I can't take the solar panels out. But this gives me some ideas for at least explaining what it does. Thank you!