Fire is the rapid oxidation of a material. Water is 2 hydrogen and 1 oxygen. Every molecule is fully oxidized. It’s also a common byproduct of fire. Therefore, you can’t burn it, because it’s already burnt
Oh man… Wait until you hear about fires hot enough that if you put water on then, it breaks the water molecule and the hydrogen molecules cause an explosion.
Look up class D fires.
Furthermore, you can burn water with a strong enough oxidizer. Oxygen, despite lending its name to the word “oxidize”, is not the best oxidizer out there. That belongs to things with fluorine in it. You can burn water with pure fluorine gas to produce hydrogen fluoride and oxygen.
Don’t try this at home. Both fluorine and the resulting HF is deadky.
HF is itself a super nasty piece of work – a deadly acid that seeps through your skin and kills you from the inside.
Flourine by itself is nothing compared to chlorine triflouride (CTF) though.
There were some ideas to use it in rockets, but, as John D. Clark put it:
It is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because of the formation of a thin film of insoluble metal fluoride that protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.
There were a few successful test fires with a CTF rocket on the ground, but to avoid explosions they had go through an elaborate multiple hour long cleaning procedure, and it ended up being too expensive and dangerous.
