A downstem is a vital component of a bong or water pipe, typically a small glass tube that connects the bowl to the water chamber. While glass is the most common material, downstems can also be constructed from silicone or metal. The main function of a downstem is to facilitate the flow of smoke from the bowl into the water, where it is both filtered and cooled before inhalation.

The key functions and features of a downstem include:

Smoke Filtration: Downstems play a critical role in filtering the smoke before it’s inhaled. As the smoke is drawn through the water in the bong, it is forced to pass through tiny bubbles. This process effectively breaks down the smoke and filters out undesirable impurities like ash and tar.
Smoke Cooling: In addition to filtration, the downstem assists in cooling down the smoke. The interaction of smoke with the water significantly reduces its temperature, resulting in a smoother and less harsh smoking experience that is easier on the lungs and throat.
Suction and Inhalation: The downstem aids in creating suction by pulling the smoke or vapor into the water before it can be inhaled. This suction process is essential for the proper functioning of the bong.
Design Variations: Downstems can come in various designs, including fixed or removable options. Some downstems have a diffuser at the chamber end, which further enhances the cooling and filtration process by creating more bubbles.

Without a downstem, achieving the desired level of smoke filtration and cooling in a bong would be challenging. Smoke would flow directly from the bowl into the water chamber without passing through any filters or bubbles, resulting in a harsher smoking experience that could potentially harm the respiratory system.