It is possible that the water has caused some of the circuting to short, and that would explain why your light does that.
If you can (and remember, this will void your warranty) open it up, try to dry it completely, making sure there is no sign of water or any stains. If you have a full coverage warranty on it, I'd suggest you get ahold of nintendo and get a new one.
If you only have a warranty that covers just the faults of the DS itself, you may have an expensive paper weight on your hands now
At least you learned a valuable life lesson though. Don't be near open bodies of water with Electronics in your pocket under any circumstances. Freak accidents happen, and simply getting splashed at random is enough to kill your expensive gadgets.
Goodbye Psypoke. Consider this my going away present.
"DERP I'M A DUMBASS :B"