We hear the terms "water cooling" and "liquid cooling" used interchangeably, and this no doubt raises the question as to what kind of liquid is actually used in these PC cooling systems. Is it just plain old water?
Out of the Tap
While most experienced liquid coolers will probably discourage you from trying to use plain old tap water in your liquid cooling system, the fact is that many people still do it that way, and like it. The obvious advantage is, of course, the fact that you don't have to find and purchase a special fluid for your cooling purposes. Water out of the tap is only a few cents. Water also has documented cooling advantages, being one of the top liquids for shedding heat when compared to other options.
What is the downside though? There has to be one, or else no one would drop any amount of money on a specially formulated solution. The fact of the matter is that water is a dangerous choice. Leaks, spills, drips, and other accidents are not uncommon in liquid cooling systems. If plain tap water dripped onto a component of a running PC, that would very likely be the end of the entire computer, or at the very least that one component. Most enthusiasts put too much time and money into their computers to risk it all by trying to save a few bucks on liquid. In spite of that, water is still very much loved for its cooling properties, and distilled water has become a popular choice.
Commercially available distilled water, specifically for liquid cooling PCs, is available. What advantage does distilled water offer over tap water? The obvious first answer is, of course, that it is purified. Distilled water doesn't contain the chemicals, minerals, and other additives so common in tap water. The impurities of tap water can rust and oxidize metal, erode rubber and plastic, and leave residue throughout your liquid cooling system. Some brands of distilled water are even rated as almost 100% non-conductive, all but eliminating the need to worry about whether leaks are going to destroy your precious system.
If the name Ethylene Glycol sounds familiar to you then it's probably because you've read it on the side of an automotive antifreeze container. Yes, you can use antifreeze to cool your computer. But should you? The toxic nature of antifreeze is well documented, and people are discouraged from using it when not absolutely necessary, largely because of the very real risk of it contaminating water sources and killing wildlife.
Various glycol solutions are available from different companies, like Thermaltake and PrimoChill. Some of these are considered to be "less toxic" and others "non-toxic". One great choice is the PrimoChill PC Ice product, which comes in a variety of colors. Unlike Thermaltake's standard liquid, PC Ice won't cause birth defects, doesn't include the number for poison control, and won't cause skin or eye irritation. It, and the color additives, are "food safe", non-toxic, and do a fantastic job at cooling your PC. It is also non-conductive, so leaks won't be detrimental to your computer. The only potential downside of PC Ice is caused by the coloring additives. These have a tendency to leave a residue, especially when it evaporates. When I wanted to switch colors I had to replace all of my tubing.