The Watts Premier Four Stage RO system begins with stage 1, a five micron Sediment filter that traps particulate matter like dirt, rust, sand silt and sediment that will affect the taste and appearance of your water. Stage 2 is a five micron Carbon Block filter that provides a reduction of chlorine, chloramine and other materials that cause bad taste and odours. Stage 3 is the heart of the reverse osmosis system, the RO Membrane. Stage 4 is a high quality GAC final filter (this is called a final filter because it filters after the membrane). The filtered RO water passes through the membrane and enters the storage tank. When you’re ready for a taste, it will leave the storage tank and pass through this fourth stage on its way up to the faucet. The end result? Crystal clear, high quality, and great tasting water!.