In a computer, water cooling or liquid cooling is a system used to reduce the temperature of its hardware, specifically the CPU and GPU. Liquid is more efficient than gas at conducting thermal energy, so liquid cooled machines maintain desired operating temperatures better than their air cooled counterparts.
How it works
The process begins with a pump that sends water into a water block. As water absorbs thermal energy, it's passed to a heat exchange (usually a radiator) where a fan blows the heat out of the computer, and the cycle starts again.