Oster Cat Fountain Filters Replacement for Clean Water, 100 fl. oz. Replacement Filters for use with Oster Fresh Sips less stress Cat Fountain 100 fluid oz Includes two (2) Charcoal Filters that reduces impurities in the water and one (1) Particle Filter that helps capture hair, food, dirt and other debris To be replaced every 2 to 4 weeks depending on number of pets using the fountain