PetSafe Drinkwell Premium Charcoal Filters are replacement charcoal filters for PetSafe water fountains. The set includes 3 pieces. The charcoal filter keeps the water clean by removing unpleasant tastes, odors, and impurities. Simply replace the charcoal filter during fountain cleaning. Regular replacement every 2-4 weeks is recommended. PetSafe Drinkwell Premium Charcoal Filters are compatible with the following pet fountain models: Drinkwell Mini Pet Fountain, Drinkwell Original Pet Fountain, Drinkwell Platinum Pet Fountain.