Well, if it has been in water for just seconds, that'd be ok, but for several hours, not a good at all. There is little hope but try to save it.
Don't try to turn it on. That would cause short circuit and could kill it
Take off the battery as soon as possible.
Dry the iPhone and the motherboard as much as possible. That won't dry it at 100%.
I guess you don't have pentalobular screwdriver to do so, thanks Apple to let our iPhone die.
If you don't have one, get the [product|IF182-019], and change the pentalobular screws for standard phillips.
I strongly recommend you to buy the [product|IF145-163] and follow the instruction [http://www.ifixit.com/blog/blog/2011/11/23/thirsty-bags/|thirsty-bag]. It would completely dry it, if it's not too late.
Change the battery.
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