Catit Triple Action Fountain Filters provide three-in-one filtration so your cat can enjoy clean and odor-free drinking water, directly from their Catit Flower Fountain. The filter’s outer layer, made of cotton mesh, catches stray hairs and other debris. Layer two's active carbon helps remove foul odors and impurities. The third, ion exchange resin filters out excess calcium and magnesium from tap water, softening it. In large amounts, these minerals can build up in your cat’s lower urinary tract, which can in turn lead to urinary tract disease.