Sure, but that's kind of missing the point. We're taking advantage of rain and rivers with the water mill. The water flows downhill and we benefit from it, yet

Sure, but that's kind of missing the point. We're taking advantage of rain and rivers with the water mill. The water flows downhill and we benefit from it, yet we don't have to do any work to get that water back uphill. We gain more energy out of it than we put in.