That's funny you mention this Frank as I was wondering the same thing the other night. I pulled that movie off the shelf and put it on while I was working on something.
At the time it came out I thought Waterworld was "so-so". After recent viewings though, I really like the movie. I think it got a bad rap in a lot of ways; they said it was a budget breaking disaster, an ego-driven Costner flop, a rip-off of other movies just on the ocean, etc. First of all, I dare someone to try filming on a ocean and see what happens to the budget. Second, it takes a big personality and someone who can think big to lead and deliver something like that to the screen and third, while it may be derivative of other stuff in some ways, it's also very original and entertaining in it's own ways. Dennis Hopper is hilarious as the Deacon.
I would bet that the cover is custom made for the movie.
;-)
Jon