Here's a cut and paste statement about water wetter from
http://www.overclockwatercool.com/water_wetter.html
"While the bottle recommends 4 oz per gallon in automotive cooling systems, extensive testing in our own systems has shown that 2 oz of Redline Water Wetter in one gallon of water is an optimum mixture for our computer cooling systems. Any less reduces its heat transfer properties. Any more just adds color to your coolant."
Just passing on what i've read and not what i can vouch for through personal experience.