The replacement filter for the PetSafe® Drinkwell® Stream drinking fountain is compatible with all sizes of the PetSafe® Stream series fountains. The filter features a double-hardened polyester fleece that captures hair and debris. The activated carbon insert also removes unpleasant tastes and odors from the water. The filter helps extend the lifespan of your drinking fountain and pump and should be replaced every two to four weeks. PetSafe® is committed to keeping your pet healthy, safe, and happy.