You're in for a nasty surprise, if you follow that idea through... you're not the first one to come up with such a bright idea!
Have a look here at Overclockers.com for reasons why:
http://www.overclockers.com/forums/s...d.php?t=373263
They have some very fine threads for guiding you through your build, highly recommended!
I'm using Feser One Cooling Fluid. That's destilled water with ethylene glycol and other good stuff.
Protects copper against corrosion and prevents algea growth... but worthless for spicing up the coffee...