Activated carbon absorbs a variety of impurities and can be used to reduce odor and taste substances, bacteria, VOCs, pesticides and general organic impurities, or to decolor fluids. There are two types: filters containing granulated carbon, and filters with porous activated carbon blocks extruded to form tubes. The maximum flow rates, contact times with the activated charcoal and thus the retention rates of these filters also depend on whether flow is axial or radial.