Water as a source of fuel is largely unproven. And even less proven in the case of powering automobiles. Some advertise around the internet and in the backpages of newspapers claiming to have a device to increase your gas mileage or power your car from water but these devices have ever been proven to be successful.
The water fuel cell is a device invented by American Stanley Meyer, which he claimed could convert water into its component elements, hydrogen and oxygen, using less energy than can be obtained by the subsequent combustion of those elements, a process that results the reconstitution of the water molecules. Thus, if the device operated as claimed, the combustion cycle would start and end in the same state while extracting usable energy, thereby violating the first law of thermodynamics and allowing operation as a perpetual motion machine. Meyer’s claims about the Water Fuel Cell and the car that it powered were found to be fraudulent by an Ohio court in 1996.