presumably when you run a charge (6v) through it, H2O becomes HHO, and somehow mysteriously, a very small quantity of hydrogen passes in a vacuum into the engine along with a lot of water I guess; You add like baking soda to the water to activate the charge (clueless here - so knowledgeable readers forgive me). Wikipedia explains it...
My question is whether their claims of up to 1/3 improvement in fuel efficiency is due to the fact that water is displacing the fuel and less fuel is going into the intake or something. Often, the oxygen sensor will sense less fuel, so actually add more gas and you burn more, unless you can trick the sensor to think all is well...