4 Stage filtration replacement. Stage 1: Sediment (remove rust and small particles), Stage 2: Pre-Carbon (remove odor), Stage 3: RO Filter (remove contaminants), Stage 4: Post-Carbon (final filtration). We made changing the filter as easy as possible with our easy twist-in replacement filter cartridges. No tools are required and no contact with the filter material is needed. It’s a clean and simple way to change the cartridge without the mess.