GE Osmonics Desal TFM-18 Reverse Osmosis Membrane Drinking water filtered by reverse osmosis provides a superior quality of purity right from the tap A replacement membrance offering 18 gallons of high quality drinking water per day Be sure to match the correct flow rate of the membrane with the flow rate of your RO system, for peak efficiency Great return on your investment: replace the TFM-18 membrane approximately every 2 years, depending on water quality and your usage