The most likely thing... and I know you're gonna hate me for saying this, but - even if you get a battery, it won't fix the phone. Because it will not charge the battery through the charger. I had a similar issue, however, I did not have any water fall on my mobile... I did buy a new battery only to have it die on me. All because the phone itself was messed up.
In this case, I would say, yes, your mobile is a goner and going through the effort of buying a new battery is not worth it. Unfortunately, you will need to get a new phone.
My phone had to go into repairs and what not for over 2 months and it was very close to the end of it's one year warranty. They then tried to tell me it was water damaged. However, they gave in, when no fault was found with it.
I hope you have better luck than I did.
29/10/2007
Only in Memories