What does everything think about the gas/h20 mix for big fuel efficiency..?

[CrackerJackToy]

I got to reading around & looking on youtube, and I noticed that using gas/h20 mix will yeild very high gas mileage increase. You must run two seperate tanks, one for gas, one for water, but should yield 20+mpg on the h2 in the city. It should also yield 28-30mpg in the city for my Corvette, if its as true as the customer testimonials.

I figured I would ask everyones opinion here, since $4 a gallon & only rising really hurts.