Think how a player would think when they load up this level. A square of water in a grey room. Fun. >.>
Try and use your imagination, perhaps, it could be made more interesting, by adding two Waterslides for sonic +co to run down, a plug hole with a sewer system, that evetually bounces the player back up. That would make it interesting, and fun.
If your stuck on any of the stuff I mention, dont hesitate to PM me. I can fix up any questions you've got etc...
Never be afraid to try new things! Thats my motto
Good luck with your wad, I hope it turns out well!