A thought just occurred to me. What kind of production do water tiles generate in Elemental? I'm asking because I'm thinking if it would be feasible to make a waterborne city, like the pirate faction in the in the expansion of Alpha Centauri.

I doubt there will be an option for waterborne cities in the release version, but it would be neat to be able to add them with mods. Someone could probably make an Atlantean/seafering/amphibian/SCUBA civilization.

In a word?  Water tiles don't produce anything.  Any more than any other tile produces anything.

Buildings produce things... though some buildings can only be built on certain tiles.