A water engine will produce the automotive power your car needs from water. The water will be stored on your car. But you will notice one great improvement in its storage. You will now store less fuel and rather get more power. The reason is hydrogen the gas that will provide the fuel for your car is required in a small amount to power your car.
A glass of water may be all your engine needs to provide you with miles of motoring. You will need small storage to hold the gas because the little produced will keep recycling for a long time. Now you can run your car on water.