Quote (goldfreek @ Thu, Apr 16 2009, 05:12pm)
Using water is not possible, but if you separate the hydrogen from the oxygen then you could run your car on the hydrogen and emit the leftover oxygen as your exhaust. This commonly referred to as a fuel cell car. Only with the fuel cell the car uses straight hydrogen and does not separate it out of the water because that requires a lot of energy.
you would spend more energy separating hydrogen and oxygen than you'd get from the burning of hydrogen.