Basic Information
A Water World is a Terrestrial Planet who's surface is covered with Water. It probably has islands, and in general the water isn't nearly as deep as an actual Ocean Planet.
All sorts of water-related terrain is likely to show up on a Water World. In addition to Ocean, Shore, Island, Archipelago, etc, you'll also probably have derelict ships, flotsam and jetsam, raft city, flood plain, underwater ruins and other signs that there used to be inhabited land just below where the water is now.
Once upon a time, the Water World had plenty of dry land. Then some sort of climate change mucked it all up. It could be global warming melted the polar ice cap - but that'd have to be a huge ice cap for the land masses to just go away. So, perhaps the current state is the aftermath of an impact from a enormous icy comet. Often overlaps with After The End.
Sources
Game and Story Use
- Let me relieve you of a few crazy notions you might have picked up from a certain movie that shares names with this trope.
- Firstly, on earth, our polar ice cap isn't big enough to cover all the dry land when it melts - though it will flood low-lying areas, there'll be plenty of islands left where high elevations are now, and most of the water will be very shallow.
- Secondly, if our planet did have enough ice to submerge all the land, that would probably dillute the salt water enough to make the oceans drinkable.
- Taken to lesser extremes than that film, or if better justified than that film, this could be a decent after the end world. And there's certainly plenty of super-science or future tech that might justify this.
- The comet idea mentioned above is tiny bit more complicated than as presented there. Comet hits - big nasty blast, and all the debris clogging the sky causes something akin to nuclear winter. Everything gets really, really, cold. The ice and dust slowly settles out of the atmosphere, and eventually the temperature returns to what it was before the comet impact. That's when it floods. So, the comet-caused water world doesn't really come about until after after the end. Unless the comet impact changed the planet's orbit or axial tilt - but then things get really complicated.