Yeah, man. That's a bummer. I had gotten a waterproof case for my s3 a while back. I was out by the pool and I had mentioned to my 9yo niece my case was waterproof. My 5yo nephew didn't believe me. So naturally, I give it to him and say "throw it in." I had been using it in/near the water all day, and no problems. Turns out when it hit the water, it hit at such an angle that the earpiece membrane was pierced by the pressure.
Here's the crazy part. I didn't even notice. It remained powered on and waterlogged for over an hour before I went to use it and it wouldst register touch (due to water in between screen and screen cover of case). I turned it on and off TWICE in this state before it dawned on me that it was full of water. I turned it back off immediately, and then did this:
(Note: This happened to my s3, but this is generally the best path of action to take with any phone that comes in contact with water)
# Took phone out of case, removed battery cover and took out the battery and sd card.
# Used paper towel to dry up whatever I could, and I believe I used my mouth sucked a bit of water out of the earpiece/microphone/usb ports.
# As I drove home, I head the phone with battery cover still off over the heat vent in my car, with heat on max.
# As soon as I got home, I cleared off a well lit spot on my table, grabbed some paper towel and a hand full of q-tips.
# Unscrewed and removed the back panel that covers the board. Water '''EVERYWHERE'''.
# Used paper towels and q-tips to carefully and thoroughly absorb every last bit of water I could reach.
# Unplugged and removed rear camera, making sure to dry up the water hiding in all the crevasses. Then I unplugged everything else from the motherboard, removed it, and carefully dried the backside.
# Took out the front camera and sensors, sucking up all the water in there that I could see. This is pretty much as deep into the phone as you can go in this situation. All that's left is the shell, LED, and glass, and that whole area is sealed up.
# Spread out all the pieces on some paper towel, and left it sitting out on the table to air-dry overnight for a solid 12 hours.
# The next afternoon, I reassembled everything. It was now the moment of truth. I hold my breath and plug the phone in to the wall charger and....'''''it booted!''''' I was very surprised, I mean, there was a lot of water in the phone. But everything appeared to work as it should... everything except the cameras, front and back.
# Order replacement front and rear cameras off amazon (they are super cheap), and figured swapping them out would fix it. Unfortunately whatever issue there was was board side, and installing brand new cameras did not fix it.
# Put an add on craigslist looking to buy a sprint galaxy s3 with a broken/cracked screen, cosmetic damage, bad esn etc. 2 days later I had a 32gb replacement motherboard I only had to pay 75$ for. Moved over my ESN/MEID, EFS partition etc. Phone works like a champ, and I also had a bunch of spare parts in case I ever needed them.
I used this method two more times to acquire replacement boards, never had an issue. I would highly recommend going about getting a new board this way as opposed to getting bent over a barrel by some !@#$% on ebay. The only thing you need to be careful of is The boards ESN status. I myself am familiar with migrating ESN/MEID and the software it requires. I always moved over a good ESN of mine right away regardless, so whether or not the board I was buying had a good or bad ESN didn't matter to me. For someone unfamiliar with all that, I would recommend verifying the ESN prior to exchanging any money. The ESN/MEID can be found on a sticker behind the battery. You can call the applicable carrier and ask them to verify the status of the serial number for you.
This is long, I know, but hopefully someone will have the patients to read it and it'll help a bit. The most important thing to do when your phone comes in contact with water is to immediately power if off and remove the battery. Once that's out of the way, the second most important thing is taking your time. DO NOT rush. If the phone has any hope of survival, it must be completely and entirely bone dry on the inside before you attempt to power it on again. I got crazy lucky, my phone should have been toast. The cameras being the only casualty is just crazy, and I have no real explanation for it other than dumb luck.
Good luck!