Replacement Filter Pack: Multi-pack replacement foam and carbon filters for the ZEUS H2EAU Pet Water Fountain. Contains 2 foam filter cartridges. Carbon Filtration: Activated carbon helps absorb water impurities and keep water tasting fresh and clean. Removes Material from Water: Collects debris, food, dog fur or dog hair and sediment from your pets drinking water. Keep Your Pet Hydrated: Ensures your dog or cat is drinking fresh and clean water at all times. Recommended Use: It’s highly recommended to change filters every 3 weeks.