The Cat Water Fountain Filter Replacement 4 Pack is a high-quality, natural filter that removes harmful contaminants from your cat’s water. Made of large diameter coconut shell activated carbon, porous weak acid ion exchange resin, non-woven fabric, and ABS grid, this filter also filters out fine particles, hair, and chlorine. With a replacement period of every 2 to 4 weeks, this filter is designed to be used in a circulating filtration system.