Well, you should never, ever try to turn on a water damaged device.

Water itself is not damaging, but it deroutes electricity where it's not supposed to do.

So, at first, you should dismantle your device and clean it throughly with isopropylic alchol. Let the parts dry, then reassemble and evaluate.

You're surely going to need a new battery: yours surely was shorted when it got wet.

After the battery change, you could check for other signs of damage.

The most common problem on the iphone 4S which has been exposed to water is battery failure. With the 3GS it is usually the LCD. Remember that the rice trick is only a temporary solution since moisture can still be trapped inside of the main board shielding. Read more about what to do with a wet cell phone here. As a previous poster said, turning the phone on is a bad idea as it causes electricity to flow through components that are still wet. This can easily short something out and cause more damage. Once you replace the battery pay attention to whether the phone gets hot while charging. This is a good sign that you will have problems in the future.