The construction of the cartridge allows water to enter at one end and pass through the entire length of the carbon bed before exiting to the other end of the cartridge, while an external expansion pad minimizes channelling or bypass. Before the water exits the cartridge, a 20 micron post filter helps reduce carbon fines and other suspended particles from the filtered water. The post-filter is permanently fastened to an innovative support basket ensuring that it is firmly secured and eliminating any potential of bypass making it suitable for drinking water, food service, and many other situations.