Fresh Flow Replacement Filter 6 count 8.3" x 0.6" x 6.1" (2 Pack) The filter reduces bacteria in your pet drinking water. The three pack will give you three months of water filtration. Double for your money. Petmate recommends replacing filters every 30 days (more often if you have more than 1 pet). The charcoal filter removes odors to give your pet fresher drinking water. Charcoal filter removes contaminants from your pets drinking water.