The Culligan D-20 water filter reduces chlorine taste and odor and bad taste and odor from your drinking water. The Culligan D-20A replacement filter cartridge has high surface area for maximum adsorption. The Culligan D-20 filter cartridge has been tested and certified by NSF International against NSF/ANSI Standard 42 in model US-600. Note: Culligan has changed the model # of this filter from D-20 to D-20A due to a design change. The contaminant reduction remains the same. The Culligan D-20 water filter life is up to 12 months or 1000 gallons. The water filter life also depends on the quality of your water and your water usage.