Water Inc. HousePure Secure Replacement Cartridge .75C HousePure Secure LEVEL 1 Replacement Cartridge for Tankless Water Heater Scale Prevention Replacement cartridge for HousePure Secure 3/4" tankless water heater filter system provides annual protection against costly water heater scaling and sediment build-up.Filter Capacity: One year or when gauge indicates change is neededMax Flow Rate: 7 gallons/minuteIncludes a filter change indicatorTested to NSF/ANSI Standard 42 for material requirements