The jar at the bottom of the hookah is filled with water sufficient to submerge a few inches of the body tube, which is sealed tightly to it. Deeper water will only increase the inhalation force needed to use it. Tobacco or tobacco-free molasses are placed inside the bowl at the top of the hookah. Often the bowl is covered with perforated tin foil or a metal screen and coal placed on top. The foil or screen separates the coal and the tobacco, which minimizes inhalation of coal ash with the smoke and reduces the temperature the tobacco is exposed to, in order to prevent burning the tobacco directly.