Petmate Replendish Replacement Filters are a direct replacement for Replendish Waterers or Mason Style Waterers. The unique external layer of polyester material captures hair, debris, and sediment. The internal charcoal element controls chlorine levels and removes odors. Before use, remove the outer plastic covering on the filter and rinse under cold water. Once the water runs clear, place the filter back in the cap section with a flat side upwards then apply the filter strap across the top. After filling the bottle with water, attach the cap and then insert it back into the base. It is recommend to replace the filter every 4-6 weeks. Each pack includes three filters and a filter strap. Fits all Petmate Replendish or Mason style waterers regardless of the gallon size.