Loosely, Myk… Waterworld should also remind you of the Mad Max movies (esp. Thunderdome), what do both of these movies have in common? Two things. They are both, dystopian post-apocalyptic settings. Which due to the apocalypse of each movie, people generally must rely on primative (internal combustion, hydraulic, pneumatic) technology and ways of life, but yet it’s the future. Sound familiar? (see first sentence of the post) So, my guess is that it’s more this juxtaposition of technology and primativism that makes you think there is a link, rather than the movie’s writer/director actually drawing from steampunk culture, which tends to be more utopian and high-fantasy with not so much internal combustion (oil) but rather thermal (conductive/convective via burning coal) energy generation.