I have a neat video (news clip) about a guy who invented an engine that runs on water... yes that is right, tap water. It uses hardly any at all and runs just great. According to the video he has a contract with the US military right now and is working on a Hummer engine that will run on water. I don't know where the video is online but if anyone wants to PM with their email address I would be more than happy to forward it on to you.
*EDIT*
Found the video on youtube, here is the linky
http://www.youtube.com/watch?v=J9iWaCMbw60