APS ULTRA Brand Quick-Twist RO Membranes offer the best consistency available. They are guaranteed to last one year on the shelf with no biological growth so storing a spare usually a good idea. Membrane flow is based on a water temperature of 77F at a pressure of 100 p.s.i. If you would like to increase the production rate of your reverse osmisis system will will also be necessary to chage the reject flow restrictor. If you do not throw enough water down the drain you will cause premature membrane failure.