Mine got water damaged when a few drops of water got into the back and I didn't think anything of it so I left it on and kept using it for about 2 weeks. Then the battery life pretty much halved which made me think there was something wrong. I sent it back to Optus who sent it back saying it was water damaged. They didn't even open it up, they just sent back a photocopy with the USB jack circled where the water damage indicator is, I still couldn't see it. So I took mine to a phone repairer place and he opened it up in front of me and showed me all the water damage which had happened around the internal memory, and just from a few drops. He cleaned it out for me and now it's fine
Might be worth taking it to a phone repairer person to get it cleaned.