CPUs today run hotter and hotter than ever before, coupled with the overclockers' desire for the fastest possible clock speed, this can lead to the some dangerous temperatures. I've heard horror stories of Athlons running at normal speed, without cooling, and burning out in less than 10 seconds.
Air cooling can only take you so far, innovative overclockers are applying more and more techniques all the time to cool their systems, including heat pipes, peltiers, refrigeration devices, and our subject, water cooling.
A water cooling rig has three main components: a water block, pump/reservoir, and radiator, all connected with hoses.
The water block is the part the attaches to the CPU(s), (or other overclocked components, if applicable). They collect water from an input on one side, distribute it over the chip and output the heated water to another hose.
DIY water cooling systems usually utilize a normal aquarium pump, the kind that needs to be submersed in water. Thus, it is combined with the system's reservoir. If the reservoir is big enough, you won't need a radiator, the water will dissipate the heat enough by itself.
The radiator is sometimes combined with a fan to cool the water running through the system.
Advantages:
- It's quiet, seeing as it can replace all your fans. The only noise would be that of the pump, and the radiator fan if you so choose.
- Eliminating fans will greatly reduce dust.
- It's far more efficient at cooling than air cooling could ever be.
- Also, it can't cool below ambient temperature, so no worry of condensation! Unless of coarse you do something extreme, like fill the reservoir with ice cubes, or put a peltier between the CPU and waterblock.
Disadvantages:
- Expensive.
- Water and expensive electronics running side by side. You better be extra sure all those hoses are fitted properly.
If you don't feel like hunting down each component individually, there are companies that sell water cooling kits, containing a radiator, pump, hoses, water block, and all the little adapters to fit it to your CPU.
As well, a company by the name of Koolance sells fully outfitted, ready-to-go water cooled cases. It has waterblocks for the CPU, video card, hard drives, and even a water cooled PSU.
Disclaimer:
If you want to build your own water cooling rig, don't follow my node alone. Read up on the subject extensively. There are many, many techniques I have not covered.