Only a retard would suggest that water is a source of energy. Water is not a source of energy. You need to spend energy to split water into hydrogen and oxygen, and the amount of energy that is returned by combining (aka burning) them again, is less, because there are losses every time you convert a form of energy into another form energy.
You can not create or destroy energy, you can only convert it. Energy in = energy out. Always. There are no exceptions
if he is using power from Car Battery to split the Water into Hydrogen & Oxygen then indirectly he is putting Load on Engine via Alternator,
so the efficiency would be less than 1%, it like a Magic Show
