Water as a Fuel

The petition is entitled Explain why water, as a totally environmental fuel source, is not in widespread use within this country? and the explanatory notes say

"Many companies have devised simple methods of breaking down water into its basic components of Hydrogen (H) and oxygen (O). A company in Canada has devised not 1 but 2 ways of achieving this. H is a very efficient fuel source and has the added benefit, when heated, of re-attaching to O making it recycleable. Why is this not the only fuel source we use? Could it be that we would have no further need for Oil, Gas and Electricity companies? How would the government recoup the lost tax revenue? Is this the true reason for the road pricing policy? Serve the people Mr Blair and not vast Corporations! Do the right thing!"

I applaud the petitioner on his ability to grasp one minor point while failing utterly to understand its implications! Even more I applaud the five other people who've signed it in the last three days, without noticing the enormous flaw.

It is, indeed, extremely simple to break water down into hydrogen and oxygen. Very simple. No need for companies to "devise methods" - you can find it in any GCSE chemistry textbook, I think.

The difficulty is that this "breaking down" takes energy. More energy, in fact, than you later get back by using the hydrogen to generate energy.

Broadly, we deal here with the first law of thermodynamics - that energy cannot be created or destroyed - and with the second law of thermodynamics, which (among other things) says that you cannot have perfect efficiency. In other words - we can't get as much energy out of a system as we put into it.

Everyone evidently needs a tame physicist to answer this sort of question before they make an idiot of themselves asking it publicly of the prime minister (who, not being a physicist, probably can't answer it without help anyway).