Pentek MicroGuard„¢ membrane filters provide reliable bacteria and protozoan cyst reduction for safer and cleaner drinking water without incorporating chemicals into the media or adding chemicals to the filtered water. These have absolute 0.15 micron rating with a 99.9% particle retention for bacteria and protozoan cyst reduction. The MicroGuard cartridges do not require USEPA registration and their effectiveness is not susceptible to common substances normally found in some water, e.g., hydrogen sulfide, natural organic matter (NOM) and total dissolved solids (TDS).