The Drinkwell Replacement Filters keep water clean and fresh. Each filter is constructed with two filtration pads; first a duo-density polyester pad that's designed to catch large particles such as hair and debris. The second carbon impregnated pad removes bad tastes and odors, making the water fresher and more appealing to drink. In-between the two pads is granulated carbon for extended filtration. Filters come in a 3-Pack and should be replaced every 2 to 4 weeks. [This is our Standard Size Filter that is compatible among all fountain models with the exception of the Drinkwell 360 Models][This filter features 2-compartments and comes in CAT ONLY Packaging]