the scroller in a mouse is a small POT / Potentiometer and I have yet to see water short one out.
the clickers or button are small microswitches and can wear out over time. also if some water gets into the switch it can connect the terminals and make the mouse act like the button is being held down untill the water dries up.
in the scroller, the POT can stop working because dust and other stuff gets into the slider contacts. usually canned air wont fix this as the POTs are realled pritty good
im not sure if www.howstuffworks.com
has anything about mouses but you can try searching them
i say get a new mouse, they are not that expensive.