Foam Pre-Filters for Drinkwell Stainless Steel 360, Lotus, Avalon, Pagoda Water Bowl (36 Filters) Provides your pet with cleaner, healthier water Prolongs the life and flow rate of the filter pump Improves filtration by trapping hair and other debris in the water Replace every 2-4 weeks, depending on usage Bulk packaged to save you money and protect our environment