Scorpion by Ronn Motors has a system that is completely safe and uses water from your garden hose to create hydrogen on demand. This 450hp Hydrogen Scorpion gets 40MPG.
The hydrogen is mixed with 91-octane gasoline to improve the fuel economy and reduce the emissions of the car’s 3.5-liter internal combustion engine.
Though it save fuels but you have to spend $150,000 for this car. Is that a great deal?