Guaranteed to fit inside all sizes of the PetSafe Current Pet Fountain (not included).Activated carbon filter is made from coconut shells and helps deliver fresh and clean water by removing foul tastes and odors. Changing your water every 2-4 weeks can improve the freshness of your pet’s water and help the fountain and pump last longer. PetSafe filters are designed with 50% more carbon for long-lasting filtration. Duo-density polyester pad helps remove hair and other debris from your furry friend’s water.