Adsorption is the accumulation of a gas or liquid on the surface of a liquid or solid substrate, as opposed to absorption, in which the encroaching substance enters the substrate’s bulk or volume. Activated carbon filter media is porous, inexpensive, and readily available for use as adsorbents, furnishing a large surface area to remove contaminants. It has a more useful surface area per gram than any other material available for physical adsorption. In fact, a teaspoon of activated carbon has more surface area than a football field.