Water Bong - Physical principles

Once the smoke has risen through the water, it is trapped in the air gap above the water. The empty space of the container fills up with cool filtered smoke. At the side of the container above the water level, there is a small hole which is kept covered up with a finger until the point when sufficient smoke has been held in the air gap. This hole is sometimes known as a shotgun hole, clutch, or carburetor, more commonly "carb". Its purpose is to allow an easy passage of air into the container when the smoke is finally inhaled into the lungs. The fresh air from the shotgun hole also further helps to cool the smoke as it is inhaled.

Bongs of more expensive design can sometimes feature ice catchers, which allow ice to be stored in the main chamber where smoke resides. This ice can cool the smoke to below room temperature, sometimes allowing smokers to intake significantly more smoke and hold it in the lungs for a longer duration.