5-filter pack for ISPRING 3-Stage Ultra-Filtration System CU-A3, Compare to Watts 531130 2 of First Stage 5 Micron Inline Sediment filter, Tested by independent third-party to meet NSF/ANSI Standard. It can effectively remove rust, and, other larger particles and solid Impurities in water.1 of Second Stage UF Hollow Fiber Technology membrane. Hollow Fiber Technology uses Standard home water pressure to push water through a semi-permeable membrane. Suspended particles and materials of high molecular weight are unable to pass through the 0.1 micron UF membrane, leaving you with only fresh clean water and dissolved minerals. 2 of Third Stage Post Activated Carbon Filter Adopting non-renewable coconut shell activated carbon with ultra-micron aperture, this carbon filter absorbs any residual chlorine, organics, humus, and odor.