Of course water flows downhill because it wants to be lower. It just is not in its nature to be able to want anything else, which distinguishes it from more flexible want-systems like ourselves.

As to the supernatural, I suggest a useful analogy is mathematical objects, like 5, pi, the complex plane, or the Pythagorean theorem. These objects are not physical; they are not made of quarks nor reducible to them, even though any concrete instantiation of them (or instantiation of a thought about them) must involve some physical process; they are non-natural even though they pervade nature. Nobody here would deny the right of mathematicians to be pragmatic Platonists who treat mathematical objects as real things that they can think about and perform mental manipulations on. By analogy, I would at least consider the possibility that theologians have a similar right to make statements about their non-physical, non-natural object of study.