Replacement filters keep your pets water tasting clean and fresh. The filter features a duo-density polyester pad that catches hair and debris. The activated carbon removes bad tastes and odors from the water to make it more appealing to drink. Filters help extend the life of your fountain and pump and should be replaced every 2 to 4 weeks. To replace the filter, put the filter in the filter housing with the black side facing the front. Compatible with the Current Pet Fountain in all 3 sizes.