WW, please don't insult my intelligence. I used to be an avid reader of whodunnit novels and hated the character who appeared in the final scene and turned out to be the culprit. I'm also aware of the "if there's a gun in scene one it should have gone off by act three" (paraphrased), rule. Maybe it's out of bullets!
When reading novels or watching films there's a degree of suspension of disbelief, where the viewer or reader enters a state of dreaming, not criticism. Critical reading is left to second run throughs. My degree was in Literature and, yes, we pulled books to pieces in relation to their themes, characters, symbolism, etc etc. But this wasn't CREATION.
Taking the example of the water running upstream - please don't insult my intellect with such a basic explanation of FACTS - a fantasy author could easily explain this, if you feel an explanation essential, by saying that, regarding h20 (imagine they're subscript) gravity behaves in a way which draws bodies of water, as opposed to droplets, upstream, requiring the people on that planet to go to mountains for water supplies, or to devise a system which forces water from reservoirs in the mountains downwards through a series of pressurized pipes.
Once thinking outside of the box begins, it presents all kinds of interesting ways to solve various issues, giving rise to more fascinating plot. Stay inside the box and that's what you'll write: just what has been written before you by better authors.
To John Carroll, just look at how much controversy your yet to be written book has generated. Go with your big world; readers won't stop arguing about it and in the process create more interest in the book. You'll be the next er.. Dan Brown