Trees turn sunlight into "tree food". They turn sunlight (which is basically nothing) into something. Maybe if we manipulated the process of photosynthesis, we could make trees turn the sunlight into other materials (and maybe in the far future we could have trees making metals for us). Thoughts?
I saw a t.v. show where they had native people boiling water. they woud put large leafs or ferns (not sure what kind of plant) over the boiling water and the evaporating water would collect on the leaves, thus making pure water.