To maintain your pet's health and well-being, regularly check your dog or cat's feeding and watering systems' parts and accessories for replacement. Petmate Replendish Replacement Filters are a direct replacement for Replendish Waterers or Mason Style Waterers. The unique external polyester material captures sediments and the internal charcoal element controls chlorine levels and odour. Before use, be sure to remove the outer plastic covering on the filter and rinse under cold water. Once the water runs clear, place filter back in cap section with flat side upwards then apply filter strap across the top. After filling the bottle with water, attach the cap and then insert it back into the base for usage to begin. We recommend rinsing the filter at each water change and replacing the filter every 6-8 weeks. Each pack includes three filters and a filter strap.