Infinite Energy

You serious?
it's the same as other stuff. you can't
the water losses power. if you pump them back to the same place than eventually you won't manage to pump them.
if it is "natural" who will agree to ruin a river or something for power? and there are more efficient ways

Or a watermill.

To parapharse Newton's Second Law of Thermodynamics, all things tend toward entropy.

congrats u invented the Wasserkraftwerk
^ not surprised you don't know about Water-Power-Generating-Stations
since there is no EN wikipedia to it lol ...

Wait, do you mean build it on the large scale?
So it looks somehow like this?

View attached image.