With everyone in a frenzy over fuel prices, all kinds of crazy devices are now flooding the market and promising to slash your gas bill by improving your mileage.  The most common claim is that for a couple hundred bucks, you can convert your existing car to burn a combination of water and gas, doubling your gas mileage! 

But are these things for real, or are they just a scam by a clever snake oil salesman?  Being a naturally skeptical person, I set out to find the truth – can you really run your car on water?   

When in doubt, I tend to turn to the laws of physics (and people who actually understand them).  These so called “hydrogen fuel cells” are actually nothing more than a simple electrolysis device that uses electricity to split water into its constituent components — two atoms of hydrogen and one of oxygen.   The gases generated by the electrolysis of water can be recombined by way of combustion to release energy.  This is not new technology – electrolysis has been around for decades. 

Sounds pretty good, huh?  Unfortunately, the first law of thermodynamics states unequivocally that the energy generated by recombining the hydrogen and oxygen through combustion can only ever be equal to the amount of energy it took to separate them.
Even worse, there are multiple energy losses involved in the generation of the electricity, the delivery of it to the electrolysis cell and then the combustion process.  We actually recover far less energy from burning the hydrogen than it took to create it!  Therefore, these magic “water-for-gas” devices actually cause your car to burn MORE fuel in order to heat the water in the electrolysis cell. 

Besides, don’t you think that if cars could easily run on water and gas that the auto manufacturers wouldn’t have jumped on it by now as a means of selling those slow-moving, large SUVs?  Just remember that old adage about things that sound too good to be true…

 (Special thanks to Bruce Simpson of the Aardvark Daily for explaining the physics.)