Just had this happen to me:
Dropped the Nexus 4 into the toilet Bowl. It was playing an mp3 at the time, and that immediately stopped. The phone was still on, after probably being under water for about 1 second. Luckly it was clean water. Well I pretty much cr@apped myself, freaked out, checked websites etc. Only had the N4 about a week.
After drying, and blowing with compressed air, I checked functionality. Everything worked fine, touch screen, power/volume buttons etc. But the sound was screwed up. Like others who have had problems with the mic (my mic worked fine) it was the only thing wrong.
But I managed to get it working 100% by looking up some Youtube vids to open the phone. Of course I turned it off, opened the phone with two little screws on the button (need a T5 screwdriver), and then proceeded to dry the inside. I also peeled back one layer of stuff from the inside, about 8 Phillips type screws inside, peel back a layer of plastic and undo all the connectors, apply the compressed air, and then left in front of a fan for about 4 hours. When I reconnected everything, everything including the sound worked!
So maybe this seems drastic, but if this is not covered by warranty, perhaps it is worth the extra effort over rice (which didn't seem to fix other peoples mic problems).
I did not try rice....
So, thats my story...
Good luck.