Originally Posted by Celemourn
let it dry out with power off and battery out. If, when it's dry, the discoloration is still there, then you'll need to have it looked at by an Apple auth. repair person. Applecare can give you names and numbers for the nearest repair guys. TURN IT OFF NOW!
Simply waiting for the water to dry out won't work. The cramped innnards of any laptop make the evaporation of water very slow. The longer that water sits on the circuitry of your machine, the more corrosion it's going to inflict.
As Celemourn said, get it to a repair person, but do it now
, before irreversible damage can be done. If you do not you'll risk bricking your expensive machine.