Well, there are a few potential problems.
Depending on the chemical makeup, viscosity etc of that stuff, it might make your pump unhappy.
Again, depending on the chemical makeup and how prone it is to separation, it could clog the microfins found in most modern cpu blocks in much the same way conventional antifreeze breaks down and glycol clogs the block.
Cost, cause its just plain hard to beat a 79 cent gallon of water.
Oh and the fact that antifreeze mixed with water performs worse in our application than pure water, and that website says that the evans stuff performs worse than antifreeze mix with regard to temperature. "The lube-oil temperature also runs 3 – 10ºC hotter with Evans but >500,000 successful conversions confirm this has no detrimental effect." So you can expect it to perform worse.
All in all that leaves you with a more expensive product that has many unknowns and is all but guaranteed to perform worse, and the only associated problem we have using water for our computers is galvanic corrosion, which can be completely avoided by not using aluminum.
