The Drinkwell® Replacement Carbon Filters are compatible with the Drinkwell® 1.8 Litre, 3.7 Litre, 7.5 Litre, Avalon, Pagoda, Butterfly, Seaside, Streamside and Sedona pet fountains. Drinkwell® Replacement Charcoal Filters keep your pet's water tasting clean and fresh. Each filter features a duo-density polyester pad that catches hair and debris, while the charcoal removes bad tastes and odours from the water making it more appealing to drink. Filters help extend the life of your fountain and pump and should be replaced every 2 to 4 weeks.