[Harry doesn't particularly think water's all THAT powerful, but he might be a bit biased in terms of personal preference.]

It's possible Pokemon are at least partly magical in their abilities. It'd go a long way towards explaining what they can do, and some of the weird elemental rock-paper-scissors stuff I've heard about.

[Major problem with that being that it'd take a whole heck of a lot of power. Harry's got no idea where it'd come from.]