You're very lucky your Iphone is still working.
Your battery was not the same lucky I guess:
You'll have to change your battery which is dead, you've two options:
-Use apple care that will steal you 80$ and will take 2 weeks
-Do it yourself, that will cost you 20-30$ and will take 30 mins
I let you choose the good option ;)
With any immersion you should always clean your iDevice. If you do not clean it properly, you are running the risk of later failure due to corrosion. Check this guide for that. Even so it was written for a 3G it all still applies to your phone. Just as The tinker says, replace the battery as well.