This four stage reverse osmosis system model 4SV comes pre-assembled for an easy installation. Stage 1, is a five micron sediment filter that traps particulate matter like dirt, rust, sand silt and sediment that will affect the taste and appearance of the water. Stage 2 is a five micron carbon block filter that provides a reduction of chlorine, chloramines and other materials that cause bad taste and odors. Stage 3 is the heart of the reverse osmosis system, it is the membrane. This semi permeable membrane is 1/10,000 of a micron and will effectively reduce total dissolved solids, sodium and a wide range of contaminants such as arsenic, lead, percolate, chromium, copper and radium. This membrane will also remove over 99.95 percent cysts such as giardia and cryptosporidium. Stage 4 is a high quality GAC final filter. The end result is crystal clear, high quality and great tasting water.