Actually, the soon-to-be-constructed ITER will be capable of a sustained nuclear fusion reaction with a net energy gain.
There are two places in molecules where energy is contained that we know how to extract. There is energy in the bonds of molecules, and energy in the atoms of molecules. For atoms, since nuclear fission is near impossible with hydrogen and oxygen, you would have to use nuclear fusion. Nuclear fusion is hard for oxygen, so it would make much more sense to just use elemental hydrogen rather than water. Water wouldn't work that well.
As for chemical energy (energy in the bonds), water possesses very little of it. An octane molecule, the kind used in most vehicular fuel, contains multiple times more chemical energy.
Uhm, it's not a possibility. Humans don't generate any energy with water.
Water has very little chemical energy, and has less nuclear potential than a lot of other molecules. Water is used in our bodies and other places for its amazing properties of hydrogen bonding and polarity, not because we get energy from it.
There is no way we can use anti-matter. It anihilates upon contact with normal matter, so there is very close to no anti-matter on this planet, and the amount that is present is impossible to reach. As for creating anti-matter, remember the Law of Conservation of Energy - you will only lose net energy. And finally, harvesting antimatter from space also won't work because we aren't close enough to a source of antimatter and the trip would cost huge amounts of energy, not to mention how hard it would be to store all this antimatter.
You guys ought to get your facts straight...