The Omnipure L5551 is a replacement water filter cartridge that contains a 5-micron sediment filter and a proprietary media mix. This is the L5551 and L5551-M1000 Replacement Cartridge for Magic Mountain Water Products Water Coolers/Dispensers such as Aquverse, Bottleless Direct, iBottleless, Brio, Clover, and Oasis. Also fits the BDX series Water Coolers. The GAC grains in this filter are very small grains of the purest form of this element obtainable known as GAC coconut carbon. The grains are much smaller than the grains of sand. They are responsible for absorbing liquid chemicals like a sponge. Without a sediment filter the little grains would become encapsulated in sediment and in a very short period, shorten its life and leave the GAC unable to absorb the chemicals responsible for bad taste and odor, rendering the GAC ineffective and useless. Avoid inferior knock offs using look-alike housings with similar model codes.