iPhone fell in water, Wi-Fi is screwed up now. Help?

open the phone and clean with isopropyl alcohol. allow to dry and then reassemble. simply drying in rice or whatever doesn't stop the corrosion or the debris from water effecting your phone long after it was in the water. water residue is white or green and clings to all the small pieces under the metal cover on the motherboard-so you'll need to take this off to clean under there.

if the wifi still doesn't work after this you could try replacing the cable (?no 5-I'm getting forgetful but its the tiny pin like connector not the square connector on top left of motherboard)

alternatively the problem may be software- are you on iOS 4? in which case try downgrading/restoring if you think the problem started about the time you upgraded...