The main difference is in the pulling and the hitting. With a gravity bong, pulling is something you do manually. You have to pull it up at such a rate that it fills with just the right amount of smoke. Pull too fast and theres not enouph has burned yet, pull too slow and it won't actually light at all. It's much harder to figure out how to get a good hit. Also when hitting a gravity bong (by pushing the bottle back down into the water) you have a chance of swallowing or breathing in water (BAD). With a waterfall, the speed of the pull is automatic based on the size of the hole and when hitting it there's no water left in the bottle so you don't inhale water.