Looks like some Japanese have worked it out:
www.engadget.com/2008/06/13/genepax-shows-off-water-powered-fuel-cell-vehicle/Having a water powered car will be great, however some people pay more for water than they do for petrol

Not sure why Jason is driving this car. Look closely at the picture. Maybe its one of the boys from Warnambool driving it? I'd rather drive a Fairlane than that little car.
I reckon chemists will work out a way to release energy from metals like iron and aluminium. Once they do so you will just chuck some iron or aluminium on your system and drive for a few thousand kms.