Shift key constantly activated

One of the shift keys (I'm not sure which one) seems to be constantly pressed down, even though nothing is touching them. Caps lock is not on or anything like that, and I had to use an external keyboard to type this which does seem to work.

I figure it's either a system problem or a hardware problem with the keyboard.

It may be unrelated but a day before the problem started I spilled some water on the keyboard, but the problem didn't immediatly present itself so I don't know if that had anything to do with it or not

I would appreciate any advice you can give me. Thanks.