No sound in speakers iPhone 4

my phone dropped in water, but everything work. but the only thing that dont work is the speaker. when i put my music on loud it kept saying its on headphones. and when i put my headphones in it work

Sounds like the same issue as on our post thread. For reference, it's at

https://discussions.apple.com/thread/2546722?start=150&tstart=0

Basically, it's a software issue and Apple may have to replace the phone. Go in now rather than later, as you'll want to address it before the warranty ends.