A downstem connects to the base of the water tube and provides a mechanism for the smoke to travel from the slide to the mouthpiece. Down stems can be made of either glass or aluminum. Glass down stems are very common. They often come with water tube units when purchased. They are also fixed length by their nature. However, aluminum down stems by comparison are a newer technology or trend. They tend to provide greater durability and are oftentimes adjustable in length. A down stem is an essential water tube component. You must have a down stem, typically, to operate many water tube designs. Glass Nation has a large selection of both glass and aluminum down stems to choose from .