Filters will fit any size Drinkwell Fountain The Drinwell Replacement Filters keep water clean & fresh and are designed to fit any Drinkwell Fountain. Each filter is constructed of two filtration pads; first a duo density polyester pad is designed to catch large particles such as hair and other debris, second a carbon impregnated pad quickly removes bad tastes and odors that make water unappealing to drink. In between the pads we have added granulated charcoal for extended filtration. Filters should be changed every two to four weeks. Filters can be purchased from any Drinkwell retailer.     Premium Drinkwell Filters The Drinkwell Premium filters feature a six compartment plastic frame that evenly distributes the granulated charcoal throughout the filter cartridge, providing for a more thorough and complete filtration process. Change your filter every two to four weeks or as needed. The Drinkwell Platinum Premium Filter will fit any size Drinkwell Fountain and can be found at your local Drinkwell retailer.