How Do I Fix My iPhone After Dropping It In Water?
If your iPhone has suffered water damage, it's important to not exacerbate the problem by the turning the phone on - this could result in a short circuit.
First remove any case or cover from the phone and then take out the SIM card. Try shaking the iPhone to see if any excess water comes off it. If you have access to a blow dryer, turn it on its lowest setting in an attempt to get rid of some of the water. Then place it in a ziploc bag of rice. There should be enough rice in the bag so that the phone is completely covered in it.
If your phone was only submerged briefly, then a couple days in the rice should be enough. You might want to leave it in for as long as a week if your iPhone was under water for an extended period. Be sure to change the rice once a day and give it another treatment with the blow dryer while you are swapping out the rice.
If this doesn't work, take your iPhone to the Apple Store. They will probably give you a deal on a refurbished phone since water damage is not covered under the warranty or AppleCare.