Run Your Car off Water!

I was chatting with the nice man who runs the photography studio near my house the other day, and somehow our conversation wandered into the environment. He proudly informed me that he had converted his car, by himself, to use hydrogen as fuel.

The mechanical engineer in me made me lean forward a bit with interest, “Really? Where do you get the hydrogen?”

“From water,” he told me.

My next thought was that he had solar panels on his garage or something to provide the electricity for this process. It soon became clear that his understanding of the system was that the electricity came from the battery in his car, which was charged by the alternator on his motor, which burned gas (and supposedly some hydrogen).

He seemed so proud that I didn’t have the heart to explain in great detail why this would result in higher gas consumption, even if it operated exactly the way he described. So, for your future reference, here’s the Coles Notes of why a “Run Your Car off WATER!!!!” kit isn’t what you should be spending your tax refund on.


This interpretation of running your car on water: also not recommended.

There’s a frustrating property of the universe known as entropy. There are all sorts of nitty gritty details for this, but for this situation, think of it as: “You’re always going to lose some energy.” Entropy is the reason that your furnace can’t be 100% efficient and why we can’t build perpetual motion machines.

Step One
The gasoline is burned and the gases expand, running the car’s motor.

  • Energy lost from: heat and friction.
  • Typical efficiency: 35%


Step Two

The motion of the motor operates the alternator, creating electricity. The electricity is stored in the battery.

  • Energy lost from: friction and electrical resistance.
  • Typical efficiency: 50%


Step Three

The electricity from the battery electrolyses the water in a tank, converting it into oxygen and hydrogen gases.

  • Energy lost from: heat (and there are other chemical reactions happening here as well, unless you have perfectly pure water).
  • Typical efficiency: 50%


Step Four

The hydrogen supposedly gets added to the gasoline and burned.

The total efficiency of this system is, optimistically, 8%. That means that the vast majority of the energy (in the form of gasoline) that goes into creating the hydrogen is a complete waste, and that you’re emitting more pollutants than if you’d just left the engine alone.

Like the scam that is homeopathy, the people selling these conversion kits are out to convince you that there’s some magical property to water that will solve your problems. I’ll admit that water has some pretty cool chemical properties, and it would be hard to picture the geology and biology of our planet without it, but at the end of the day, water is just…water.

3 Responses to “Run Your Car off Water!”

  1. Ian Monteith says:

    Thanks, that clears up a big question I had about those kits. :)

  2. Renshia says:

    A lot of the time these things greatly increase the level of humidity in the engine as well. This causes all kinds of problems and can create huge repair bills. ie: new engines.

  3. Absolutely, these kits are a waste of money and likely to damage your car in any number of ways. An incorrectly modified fuel line, for instance. I did see one that promised it wouldn’t void your car warranty “because you can just take it out!”

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  • Marion Kilgour

    Marion is a mechanical engineer, and also works to promote critical thinking and scientific literacy through local skeptical and atheist activism in Edmonton, Alberta. Marion especially wishes to encourage girls to consider science or technology-based careers, and is involved in the University of Alberta's Women in Scholarship, Engineering, Science and Technology (WISEST) project.