Granular activated carbon (GAC) generally is an organic carbon filtration media — wood, coconut shells, coal or peat — used for water purification, typically applied in a fixed bed application.
A filter with GAC can remove certain chemicals, particularly organic contaminants, from water, as well as chemicals that produce odors or tastes to water such as hydrogen sulfide or chlorine. Granular activated carbon notably assists with the removal of per- and polyfluoroalkyl substances (PFAS), which have become an increasing contaminant of concern for regulators.
Other chemicals, specifically iron and nitrate, can not be removed with GAC. GAC should be changed based on contaminant levels and water use, as higher levels or use may require more frequent change-outs.