Water damage on this machine has required at least a top case replacement on every one I've seen. Your's may also need the MagSafe Board replaced (which is what I would do first). After replacing the MagSafe board it may start up if the power button has not shorted out and the logic board is still good. Refer to this question for others that have had a similar problem:
http://www.ifixit.com/Answers/View/60321/Need+someone+to+clean-replace+top+case+w-+keyboard