Activated carbon absorbs waterborne impurities. Carbon has been used for thousands of years - the ancient Phoenicians (1200 BC) stored water in charred barrels for long sea voyages. Carbon is "activated" with heat and oxygen to create tiny pores, which increases the surface area. GRAYL's purifier media incorporates ultra-powdered activated carbon throughout the filter, creating an even higher surface area than in most activated carbon filters available. GRAYL's carbon is made from natural coconut husks and adsorbs a wide range of impurities commonly found in tap water, including various metals, organic molecules and industrial and pharmaceutical chemicals.