BLUONICS 12 pc Replacement Water Filter Set for Our 4 Stage UV Under Sink Filter System. Sediment Carbon Block GAC UV Bulb This is for 3 sets of size 2.5" x 9.75" replacement pre-post filters and 6W UV Replacement Bulbs that fit a standard Reverse Osmosis System or any Standard 10" Housing Unit. The Sediment filter is the first filter of your water filtration unit. Sediment filters are used to remove particles such as sand, dirt, silt, and rust. To remove these particles it allows a better performance for the following Carbon Block or GAC filters. Granulated Activated Carbon (GAC) filter adsorbs and removes bad taste and odors. Also a large variety of organic contaminants such as chlorine, pesticides, herbicides, insecticides, trihalomethanes, and many other chemicals. Carbon Block filter. Removes chlorine, bad taste and odor, organic solvents and organic chemicals that contribute to bad taste and odor. Ultra Violet Light. Kills harmful Bacteria, E Coli, Viruses Fungi, Algae most microorganisms including cryptosporidium and giardia, and many other contaminants.