The Thirsty Car?

I just came across an ad that promotes a manual on how to convert your car to run on water, or at least partially on water. Seriously. So I Googled the subject and turned up a whole slew of articles and even videos about it. Huh. Now, I haven't actually read up on the specifics, or dug very deep, but the mere fact that I didn't turn up any sites that call this a hoax is comforting. One site voiced the same doubt and came up with promising results, but didn't go into much substantiated detail: greentchgazette.com

It sounds almost too good to be true and there must be a catch, mustn't there? But lordy, wouldn't it be exciting to no longer be so dependent on gas to get around?