Brita 35503 Pitcher Replacement Filters The Brita Pitcher Replacement filter cartridge fits the Brita Pitcher Classic, Riviera, Slim models and other Brita products that call for the OB03 filter cartridge. The cartridge needs to be replaced every 40 gallons or 2 months if used with water cooler 2 filters are required and they should be changed every 80 gallons or 4 months.