The American Plumber WROR Replacement Filter Kit for the Series 3000 and 3500 Reverse Osmosis Systems. Kit includes 3 Pre-filter (D-15) Cartridges and 1 Post filter (D-20) cartridge.
The D15 cartridge needs to be replaced every 3 months. The D20 filter should be replaced every 12 months. Part number for WROR Replacement Kit is 155923-43.