The video above shows a man using water to fuel an Onan generator, a welder/cutter, and his car. It sounds amazing but there are a lot of reasons why it is not as magical as it sounds. You use the process of electrolysis to break down H2O into HHO allowing the engine to run off of hydrogen. After dealing with batteries for a few years I definitely don't feel that hydrogen is a "safer" fuel than gasoline or diesel like the video is saying. Hydrogen is safe while in a tank but can be explosive when exposed to oxygen. The main issue is that electrolysis requires electricity. You are using electricity (which may not be generated in a clean way depending on where you live) to convert water to HHO to fuel an engine to turn a motor or transmission etc. Any time you convert power you experience an energy loss (otherwise we would have perpetual motion). If you skipped the middle man and just used the electricity to power the motor then you would eliminate a point of energy loss and the need for keeping a hydrogen bomb under your hood.
I still think it is a super cool concept and may be a better fuel source for a welder or cutter.
Long story short: It takes a lot more energy to produce the HHO than it actually ends up providing.
Added note: I feel it's necessary to emphasize how ironic it can be to use (dirty) electricity produced by a coal fired generator in order to avoid burning (cleaner) fuel in your car. No I am not saying the world should be powered by diesel! I think there should be more focus on using energy sources that already exist (hydro, wind, solar) and when you have a sustainable source you don't need to worry so much about energy loss during conversion. I guess I am lucky to live in an area where the majority of the power is hydro but I am aware that there are still so much reliance on oil and coal.