These filters keep your pet's water tasting clean and fresh. The activated carbon, made from coconut shells, filter the water, making it more appealing for your best friend to drink. It is recommended that you replace the carbon filter every 2 to 4 weeks. Trust PetSafe to help keep your pet healthy, safe and happy. The filters remove any unpleasant odors or tastes from your Pet's Water making it fresher. The activated carbon in the filter keeps your pet’s water clean by removing bad tastes and odours. The duo-density polyester pad in each filter catches hair and debris, making cleaning of the fountain easier. PetSafe filters contain 50% more carbon than generic brands for superior and longer-lasting filtration. Filters help extend the life of your fountain and pump, and should be replaced every 2 to 4 weeks. The only filter brand guaranteed to fit the PetSafe 1.8L, 3.7L, 7.5L, Butterfly, Avalon, Pagoda, Sedona and Streamside Pet Fountains.