Water in a computer? Sounds crazy, but enthusiasts often do crazy things in the name of performance. When it comes to moving heat, density is king, and water beats air by several orders of magnitude in volumetric heat capacity. Now, with that physics-jargon-laden sentence out of the way, let's talk a little more about how water cooling works. Anyone in the cooling business should be familiar with the benefits of using liquids as an exchange medium. This is especially true in the automotive industry, where fluid-cooled engines are far more common now than air-cooled varieties. Liquid cooling is also picking up steam (ha!) in the HVAC industry, where geothermal systems utilize water's excellent thermal characteristics to harness the constant temperature of the Earth. Thanks to the use of a superb heat mover like water and a heatsink as large as the Earth itself, common heat pumps and blowers can manage the temperatures of entire buildings with huge increases in efficiency over traditional furnaces and air exchangers. In a computer, the principles are all the same, but the scale is a little smaller.