I have dealt with an iPhone 4 that's been into the water 2x. As others have suggested, put it into rice -- it helps absorb moisture. I also recommend putting into an oven as long as you can set to temperature to 150 degrees F or less.
The first time, it worked when we pulled it out of the sink water. Turned it off, into the rice, and waited 2 days.
The second splashdown was into the toilet. It didn't work when it came out. After rice/oven, and then after about 18 hours, plugged into a charger, it came back to life.
[Update - now 8 days later it seems to be fading. Fortunately we've been able to back it up.]
While getting the moisture out is key, water in and of itself is probably not much of an issue in these situations -- it's the stuff that's in the water. Any contaminants, including minerals that are part of your water supply, could be a long-term problem.