Pentair GRO-50EN High Efficiency 50 GPD Encapsulated Membrane. Most reverse osmosis membranes have a 3 to 1, 4 to 1 or a 5 to 1 ratio. That means for every 1 gallon of purified drinking water made 3, 4 or 5 gallons goes down the drain. This super high efficiency membrane is a 1 to 1 ratio, 1 good gallon to 1 bad gallon.  You will save $100’s a year compared to buying water and help the environment. Go "GREEN"