Rinnai’s Scale Control System is installed on the cold water line prior to installation of a tankless water heater to provide limescale and corrosion control by feeding a special blend of compounds into the water stream. Over time, the scale control product is depleted, and the translucent cartridge will indicate that a replacement is needed. Cartridge life depends on cartridge size and water usage; however, in most residential applications, a cartridge typically lasts 10-12 months. www.rinnai.us