The D-20A Basic drinking water cartridge provides 12 months/ 1,000 gallons of refreshing drinking water by reducing chlorine and bad taste. The D-20A is compatible with the following systems, US-550, RO-2127 and US-600A. From the Manufacturer Culligan D-20A Level 1 granular activated carbon drinking water filter cartridge reduces chlorine, bad taste and odor. It has a high surface area for maximum adsorption and has a filter life of up to 12 months or 1000 gallons. This filter cartridge fits model numbers US-550, US-600, US-560, US-560K, CTR-210, SY-5167, and RO-3167 Plumbed-In Reverse Osmosis System. The filter is NSF Certified and a 2 year warranty. It also includes a change reminder sticker and is recommended for city and well water supplies.