Replacement RO membrane for the NEW #1935-3, Nature's Spring RO unit. This is a polyamide reverse osmosis membrane that can produce 35 gallons per day at 60 psi. NOTE: The RO Membrane does NOT need to be replaced every 12 months like the pre and post filters. They can last 2 to 4 years depending on the quality of your source water. To verify whether you need to replace your membrane use the R.O.P.E. test kit (stock# 1747-5)