GAC Replacement filter. Can be used in countertop and undercounter housings sold at Highwater Filters.

What is granular activated carbon (GAC)?
Granular activated charcoal is made from raw materials (such as coconut shells or coal) that are high in carbon. Heat is used to increase (activate) the surface area of the carbon; this is why these filters are sometimes referred to as “charcoal” filters. The activated carbon removes certain chemicals that are dissolved in water passing through a filter containing GAC by trapping the chemical in the GAC. However, other chemicals, like sodium or nitrate, are not attracted to the carbon and are not removed.
(from MN Dept of Health webpage)