Not to defend my uncle (the ass), but....

Despite what my mom says, I don't think he watered her book on purpose, even if the same thing DID happen last year.

A. If it happens once, don't leave your book on top of plants-to-be-watered next time.
B. Given that he also watered his own open window, very nearly hitting his own computer and printer, I think we can safely blame stupidity instead of malice.

Besides, we have another copy of that book at home. (And it isn't the best Meg Landry book anyway.)