It'd be a violation of the 2nd law of thermodynamics? What sort of energy does he expect to extract from the water? Is he going to split it back into H2O and

It'd be a violation of the 2nd law of thermodynamics? What sort of energy does he expect to extract from the water? Is he going to split it back into H2O and then burn the hydrogen? That just results in the same amount of H2O that you had to begin with (assuming 100% efficiency). The only way a car could run purely on water is to get the H to bond with something more chemically reactive than Oxygen, and that's just not possible since you're just running on water. Look at the periodic table. There is just ONE element more electrochemically negative than Oxygen, and it's Fluorine. So unless he's planning to make a car that runs on water and Fluorine, it's not possible. http://en.wikipedia.org/wiki/Electronegativity http://en.wikipedia.org/wiki/Electronegativity The one other alternative is fusion, and I'm sorry bud, but it ain't happening in a car anytime soon.