1-Year Filter Replacement Kit for PuROTwist 4000 with 50 GPD TFC Reverse Osmosis Membrane and FREE Replacement Large O-Rings as CourtesyINCLUDES:STAGE 1 – 1x Sediment Pre-Filter (Q5605) – Replace every 6-12 months or as neededSTAGE 2 – 1x Carbon GAC Pre-Filter (Q5633) – Replace every 6-12 months or as neededSTAGE 3 – 1x RO Membrane TFC 50 GPD (TQ56-50FC) – Replace every 24 monthsSTAGE 4 – 1x Carbon GAC Post Filter (Q5633) – Replace every 6-12 months or as needed*Filters may need to be replaced more often than indicated depending on incoming water contaminant level and volume of water being treated.