It would probably depend on the fountain. For example, the fountain in our local mall collects the money monthly and donates it to various charities. If you climbed into that fountain and took the money, you'd probably be arrested for theft.
Otherwise, I'd go for it if I were you.
Haha... I'm not
that big a douche. If I really wanted to fuck with them, I would just take all the money and donate it to a different charity.
But hell, I may as well do it.