My friend, Mavis asked if it was true. I replied as follows.
I think, Mavis that the water is split into hydrogen and oxygen by electrolysis (a process called electrolysis) and the hydrogen is then burnt in the engine.
Of course, the electricity has to come from somewhere. And that somewhere is almost certainly a fossil fuel source (oil, gas, coal, nuclear). Ideally, the electricity comes from solar panels. But they come from manufacturing that uses fossil resources in the main.
In addition, the electrolysis of water requires an added ionic material: sulphuric acid is used in school, demonstrations of the electrolysis of water, for example.
Overall, these 'magic' solutions are not the way forward.
First we need, in the global north-west to reduce our GDP activity (ie our capitalist 'economic' activity: the '' marks signify that most capitalist 'economic' activity is harmful and not beneficial to the global household).
Secondly, that activity in the global north-west needs to include far greater income and economic equality and equity (the evidence in, say, The Spirit Level, is that more equal societies act more sustainably: partly because their populations have less 'need' for status bling).
Finally, the overall poorest countries need a) to not be hand-bagged by the global north-west's capitalist businesses (including ususry-based for-profit banks) and b) they need to be helped to come up to the 'contraction-and-convergence' sweet spot that is the dog-leg point on the GDP-vs-Wellness graph in The Spirit Level.
All of the above is, of course, in the plan for Co-operative Socialism!