A water cooling system is a means by which to remove heat from your CPU. It will generally cool your CPU better than a air cooled system because the heat is removed from the CPU then transported to another location to be cooled. The benefits of this is that the water can be cooled by a much
larger radiator than can be practically connected directly to the CPU.
Water cooling systems typically consist of four parts:
The water block is connected to the CPU and is responsible for transferring the heat from the CPU to the fluid. Once the fluid has been heated, the water is transported to the radiator by the pump. Once the heated fluid reaches the radiator the water is cooled by air (in most cases) and returned to the water block.