Well if water drips of your video card, which is normally right below your WB, you'll notice artifacts all over your screen, it's not pretty. I've had water drip on my sound card before and not had a problem, but thats not to say that nothing will happen. I think alot of people put suran wrap or somthing like that on top of thier cards to prevent leaks from doing any damage. Another good sign that you're loosing water is if you have a T-line or reservoir and the water level declines at a high rate. Water will evaprate anyway, so don't mistake that for a leak. Leaks can also suck in a little bit of air, so if you see a rise in temps or little bubbles, look to see if you've got a puddle somewhere.