It is best to change prefilters every 3-6 months to protect the membrane. This is dependant on the ammount of water you pass throught the unit and how much sediment is in your tap water. The more water you produce the shorter the lifespan of the pods.

The membrane should be good for many years if prefilters are replaced as needed and the unit is kept wet and flushed. The best way of telling if the membrane needs replacing is to use a TDS meter, this will give you a measurement of the quality of the water coming out allowing you to see when the membrane is no longer performing. When replacing the RO membrane always replace the flow restrictor to keep the optimum rejection rate.