The 3MROP416-20A 3M Undersink Reverse Osmosis Replacement Filter Cartridge is a replacement cartridge for the 3MRO401 and 3MRO501 Under Sink RO Systems. This filter reduces chlorine taste and odor that can cause unappealing smell and taste along with cysts and select VOCs. The slim profile of this filter helps minimize the amount of space your system takes up, allowing for more under sink storage and convenient accessibility. 12 month filter life makes maintenance a breeze. With easy change connections and easy installation the 3MROP416 will have your system back up and running in no time.