Pentair 50 GPD TLC (Thin Layer Composite) RO Membrane and Pentair 75 GPD TLC RO Membrane provides high quality water for a broad range of water chemistries. As matter collects on the membrane, water from the feed solution sweeps it away and out its own tube. The cleansed permeate, or purified water, stream continues separately from the drain stream to a storage tank or its point of use.