Noctua is showing off its pumpless water cooling concept at Computex, and it's very bubbly
Bubble, bubble, cooling's no trouble.

Water cooling is a great way to keep your components cool, but there are a few key components that need to work in tandem to keep everything running smoothly. One of them is a pump that cycles the water through the system, so that the cold water can reach the components that need cooling down, and the hot water can be directed to a radiator to be cooled back down.