Another scam. It takes far more electricity to split water to Hydrogen and Oxygen, than using it on an electric car. Electric cars consume electricity at a rate of around 0.25 KWh per km (Tesla Model S gives a mileage of 6.25 km per KWh). On the other hand, around 10 KWh per km will be required for these Hydrogen-powered cars.
Well he's explanation is quite reasonable. Actually I'm not good in mechanical but if water can power a car, it was invented by now. Water can be use in a car as 1 of the tool to power a car, not water alone.