Rainfresh ceramic water filter cartridges are very fine micro-filtration cartridges that are designed to remove coliform and other pathogenic bacteria (such as E. coli), parasites, cysts and fine particles down to 0.3 micron. This makes them an excellent choice for use with untreated waters such as lake, river or well water to deliver clean, safe and pure drinking water. Rainfresh ceramic water filter cartridges offer unparalleled performance in the production of safe drinking water. Independently tested, they remove > 99.99999% of harmful bacteria and >99.95% of protozoan cysts (such as Cryptosporidium & Giardia).