You suspend the pails over top of each other, put the stuff you want cooled in the bottom pail fill the top pail with water, hang the chees cloth so it surrounds the bottom pail and is in the water on the top pail and the whole thing works like a capiliar action based evaporation cooler.

I've never tried it because most of the times I'd want to use it the humidity was so high it wouldn't work well, but if you are someplace drier....

they have a voracious appetite for compressed air, although the cold side can and does go well below freezing and the hot side will burn the skin off of your fingers.

they really are quite useful and are a great alternative if you have alot of compressed air available.

perhaps a water pumping mill connected to an air compressor head. most of those mills have incredibly low wind speed start up and very good torque.

might make for an interesting project for someone so inclined

The unglazed earthenware olla, a large crock or jar, was used for generations in Southwestern parts of the United States where Spanish language and culture predominate, particularly in South Texas and California. The olla was usually used to store water on a patio and was wrapped in burlap to keep the water cool.

If I recall correctly, I read that water seeps through the clay olla and evaporates, keeping it cool.  If IRRC.  I probably read this in a Louis L'Amour novel.

http://www.city.toronto.on.ca/water/deep_lake/