Our Aqua Pure Flow system is a 5 stage RO system. This unit starts with polypropylene sediment pre-filter to remove sediment and debris. Then, the water will go through (2) carbon block pre-filter to eliminate the chlorine or Volatile Organic Chemicals in the water. Following this pre-filtration the water forced through a semi-permeable. This is what is doing most of the purifying of the water. The product (good) water is then sent to the storage tank while the concentrate (bad) water is sent to the drain. When water is called for at the faucet, the high quality water that is in the storage tank is sent through a final Granular Activated Carbon polishing filter, which freshens up the taste for your drinking.