The Watts Pleated 20'' Big Blue Cyst Filter Cartridge (Watts FM-BB-20-1A) is a 20"L x 4 1/2"D pleated water filter replacement cartridge used primarily in whole house water filter systems to reduce cysts (99% of Cryptosporidium and Girdia) though it will also reduce other contaminants such as sediment, dirt, turbidity, limescale, rust, sand, silt, and other common particulates down to the 1 micron level. This Watts Flo-Max Big Blue pleated water filter uses advanced synthetic pleated polyester filtration technology for a larger filter surface area, longer cartridge life, higher flow rate, greater dirt holding capacity, lower pressure drop, and more efficient cyst and sediment filtration when compared to other filters which use different types of filter media such as resin, melt blown, spun, string wound, etc. The 100% synthetic cellulose-free pleated polyester media does not contain binders or additives. Because it is a Big Blue/Full Flow filter with a large diameter (4.5"), the Watts FMBB201A features higher flow rates than standard diameter (2.5") filters. Watts Flo-Max 20" Pleated Cyst Big Blue Water Filter Specifications (FM-BB-20-1A): Micron Rating: 1 Micron Max. Pressure: 40 PSID Filter Life: Approx. 6 months Temperature Range: 40 - 140 F Dimensions: 20"L x 4.5"OD (Big Blue/Full Flow) Filter Media: Cellulose-free synthetic pleated polyester Max. Flow Rate: About 15 gallons per minute (15 GPM), though it varies according to the specific filter system used This Watts pleated filter is a compatible replacement Big Blue cyst filter cartridge for similar Big Blue pleated filter brands of all types including Pentek filters, Ametek filters, Culligan filters, Whirlpool filters, US Filter filters, Ace filters, American Plumber filters, Bruner filters, Plymouth filters, Pentair filters, and other name brands. It will fit all whole house filter housings which use a 20" x 4.5" Full Flow water filter replacement cartridge.