Actually, this is a possibility.

Take a large piece of cloth - the heavier, the better. A leg from a pair of jeans, or a heavy shirt, would work.

Form it into a pouch, and fill it with water, which you begin heating.

The water will strain out, but maybe it'll be slow enough that there'll be some left in the end.

If not, start piling stuff up on the perimeter of the pocket - fine clay would work, although some kind of animal fat or grease, or even vasoline, would probably be better. This would prevent the water from dribbling out the bottom.

And if that fails, like I said before, drink whatever you can get.