How to run your car on water

I know it sounds crazy but I have been seeing stuff about it in different corners of the web. Does anyone know how to run your car on water? I would really enjoy sticking it to the oil companies and running my car on something, anything, cheaper than gas. Naturally water sounds like both a cheap and clean alternative to gas. Has anyone had experience in this technology or know exactly what the mechanics of this involve? I would like a little more detail on this before I plunk down some hard earn coin. Until someone answers my questions I shall be seeing what I can find out on my own.