Before anything, DO NOT TURN IT ON, PLEASE!
We have all been there. Do not worry. Seriously!
If you are lucky, you are reading this post before attempting to run any stupid attempts to make the water inside your iPhone vanish. Water is unlikely to evaporate from your iPhone whether you curse, cry, pray or desperately fail to disassemble your iPhone and break something in the process.
If you dropped your iPhone in water for a brief moment. Chances are high your iPhone is still alive. PLEASE DO NOT TURN ON YOUR DEVICE for whatever reason. If you do, you will likely cause a short-circuit and will brick your iPhone possibly forever.
Things to do:
1. HIT yourself for being so stupid
2. Kiss it, gently put it on your pillow and pray so hard
1. Turn your iPhone off if it is still on
2. Get a blow-dryer, set it to medium, and blow hot air for no more than a 10 minutes. Extended amount of heat in the iPhone might damage the wiring, be careful
3. Put your phone in a bag of uncooked rice, for at least 2-3 days. Take it out every day and dry it using the blower.
4. If there is water in the camera or in the screen, you should open your iPhone and blow hot air on the internal components.
5. The easiest way to open your iPhone (3G, 3Gs, 4) is to follow this guide
6. If you find water on the inside, blow it with hot air. Only remove number 1, 2, 3 to detach the screen. Carefully blow air and make sure all water is gone in this stage. Reassemble your iPhone
7. Water in this stage must be gone. Connect your phone and try to turn it on
This fix applies to all gadgets and not just the iPhone
Let me know if this works out with you. If you have any questions, please do not hesitate to use the comments section.