Waterworld

The setting is the future, in a post-apocalyptic world where water covers the world's surface. The surviving people live their entire lives on the sea. For them, dry land is just a myth.

The Mariner lives his life as an ocean nomad, 'a drifter' sailing the seas in his customized trimaran. He lands at an Atoll, a man-made island of girders covered with rusty iron sheeting. His aim is to trade some flasks of soil (a precious commodity) for supplies. The Atoll dwellers ask him to mate with a female to help prevent inbreeding, but The Mariner refuses. A fight ensues, during which it's found out that The Mariner is an evolved mutant with webbed feet. The Mariner is slammed into the Atoll's jail, and sentenced to be recycled in the Atoll's cesspit.

The only people that can help him are two other misfits on the Atoll, Helen an attractive headstrong woman, and her charge Enola. Enola has a large tattoo on her back - perhaps it's a map showing the way to dry land.