If we assume that the water damaged the keyboard and you want the keyboard to work, the best thing to do would get a replacement. You could order one from Sony, or you could look on eBay to see if anyone is selling parts that would work. (If you try that, see if you can find out from Sony what the part number is for the keyboard and if there are any procedures for replacing the keyboard. These will make it easier for you if you are looking for a used part from eBay).
If you want to use the computer for now, see if you can connect a PS/2 or a USB keyboard to the laptop. I know that hamper's the laptop's portability, but assuming they work, it'll get you by until you can come up with a better solution.