Dannye, it is possible to waste/destroy water, though not in the way you're thinking (and not in the way Greenpeace would like you to think). Tainted water is relatively-easy to reclaim, but water which has been split through electricity can only be recovered if you manage to capture the hydrogen before it escapes into deep space. So don't dump any fully-charged car batteries into the ocean, since not only would that be Bad (putting lots of fun lead and sulfuric acid in our ecosphere) but it'd dissociate a lot of water into oxygen and hydrogen.

This is also why putting a live wire with a strong AC into water results in an explosion - on one cycle, the water is heated and dissociated with one polarity, on the next the water is heated and dissociated with the other, meaning that you have, 60 times a second, very hot oxygen and hydrogen being put in the same place, where it quite happily burns, releasing all the energy which went into dissociating the water as it returns to a state of higher entropy. End result: The electricity is very efficiently converted into pure energy, and you get to find out how much energy there really is on a power line.