Keep your pet's water as fresh as possible with Petmate® Fresh Flow II® Replacement Charcoal and Debris Filters. This set comes with 2 charcoal filters that remove bacteria and impurities from your pet's water and 1 debris filter that removes any small pieces of debris in your pet's water. This Replacement Filter set is specifically made for Petmate's Fresh Flow II Water Fountain in sizes medium (110 oz.) and large (170 oz.). For best results, change filters every 2-4 weeks.