The script for Waterworld was originally written for B-movie maven Roger Corman who passed on it because he felt shoot a movie on water would prove to be too expensive. It's a pretty good movie. After the theatrical run, foreign sales, and home video, I bet it'll even come close to breaking even. It's the future and the polar ice caps have melted and the world is covered by water.
Dirt is the most valuable currency here, though they never explain why.
I guess they have yet to learn how to harvest kelp and need to plant their greens in order to round out their diet. The first half of the movie is the best. The Mariner is a great character, too. I was more than happy to watch him survive in this future world. Too bad the plot had to come crashing in.