Think of a water bong as a shower surrounded by a tube. Towards the bottom of the tube is a powerfull fan pushing air up helping evaporation. With all the heat evaporating the water becomes cooler than air temp. There is also some physics invloved with the water being cooled by it velocity and friction of the air. At the bottom of the tube is a powerfull pump, which pumps the water to the water block and then back to the top of the tube. Do a search and you will find tons of information. I have not seen him in 2 years, but PePsi posted alot of stuff on bong. Do a search for his posts.