A pool/waterfall in a BP enclosure would first off be wasted on a BP. BP's do not "like" water. They do not soak in water unless they have mites or no where to hide, and they do not enjoy swimming. In the wild they live inside rodent burrows and termite mounds in grassy savannas, they are not tropical snakes. They like some humidity, but not water or mist.
Also with a waterfall you are talking about some major maintenance.
I would not recommend anything more than a decently sized water bowl for a BP enclosure.