They dont use water - you use a non-conducting liquid - most are not only non-conductive and non-corrosive, but also biodegradable. They also tend to have much higher abilities to transfer heat than "pure" water. Water alone has a 25x higher ability to move heat than does air.
Guys, this is said with all due respect - ie I am not trying to be an A$$, but the attitude toward liquid cooling is a bit archaic. It did used to be a quirky and difficult thing. But that was years ago. Just like everything else, it has matured.
The idea that liquid is only for overclockers isnt right either. Why do most PC components fail? HEAT! The fact is that in a "standard" gamers rig - someone who doesnt overclock but just builds a sweet machine to play on - liquid cooling will often cut temps anywhere from 25-50 percent. Sure liquid is great for overclocking - but for the guy running a high end system - its very good too. The drawbacks are its not as easy to install - takes patience and attention to detail. The positives - no monthly cleaning of filters and fans, just a once a year tank fill - along with components that LAST LONGER since they are kept COOLER.
Liquid cooling is not for everyone and every application. But if your going to build a box for gaming - your well served to look at it as an option!
A couple of helpful links:
http://www.tomshardware.com/reviews/...r-pc,1573.html
www.xoxide.com