My understanding is that in the "water powered" cars, when the water is electrolyzed to hydrogen and oxygen, it is done with electrodes that are made to vibrate ultrasonically. The ultrasound causes "cavitation" of the water adjacent to the electrodes.

Ultrasound cavitation is the formation of vacuum bubbles in the water. It is known the the collapse of these vacuum bubbles produces flash of light. Why this occurs has never been fully explained. I also don't think anyone has ever bothered to determine quantitatively whether the amount of light produced in the flash can be accounted for by the energy released in the collapse of the bubble. I believe that the light flashes represent the extraction of zero point energy from the vacuum in the bubble during the collapse.

If this occurs adjacent to an electrolysis electrode it could contribute to the splitting of water into hydrogen and oxygen, so that much less than the theoretical amount of electrical energy would required for the electrolysis. This could allow for the over-unity production of electricity when the oxygen and hydrogen are recombined in the fuel cell, due to the entrainment of zero-point energy into the overall process.

I think this approach has been taken in an attempt to obscure that fact that zero point energy is the actual power source in "water powered" cars, but obviously the energy cartels are not so easily fooled, and have suppressed the technology anyway.