You could try using a known-good external USB keyboard, either an Apple or generic PC should work.
To use non-Apple non-Mac keyboard with Mac OS X and Macintosh, see this MS support article:
• Keyboard mappings using PC keyboard on a Macintosh:
https://support.microsoft.com/en-us/kb/970299
An Apple support article which replaced a more helpful one, still has generic details in reverse logic:
Use your Apple Keyboard in Windows with Boot Camp - Apple Support
And then if you have access to a second computer that can be used to see yours, if the above keyboard
can only get you into the damp computer as far as Target Disk Mode, you could try & copy content off
the water-damaged laptop to another computer or through another one, copy to a USB flash or other drive.
OS X Mountain Lion: Transfer files between two computers using target disk mode (conditional, most OS X)
In any event...
Good luck & happy computing! 🙂