The most important thing is to get the water out of your iPhone once it's dropped into water. Here are some useful tips to help you dry out your water damaged iPhone:
1) Fish your iPhone out of the water as quickly as possible.
2) Turn if off immediately if it is still on.
3) Dry it off with a towel or something similar.
4) Remove the battery, SIM card etc off the phone.
5) Put iPhone in a bowl of rice or in a bunch of silica packets.
6) Bury the iPhone and wait for a day or two.
If you are lucky enough, you may get your damaged iPhone back in working order after 24 or 48 hours. If not, get it to maintenance center to repair.
Source page: [http://www.recovery-ios.com/recover-water-damaged-iphone-data.html|How to Fix Water Damaged iPhone]