The PetSafe® Drinkwell® Replacement Carbon Filters are compatible with the PetSafe® Drinkwell® 1.8 Litre, 3.7 Litre, 7.5 Litre, Butterfly, Pagoda, Stainless 360, Sedona, Seaside and Streamside Pet Fountains. These filters keep the pet's water tasting clean and fresh. The activated carbon, made from coconut shells, removes bad taste and odours from the water, making it more appealing to drink. It is recommended to replace the carbon filter every 2 to 4 weeks.