This Cigar Oasis water cartridge is designed for the Cigar Oasis Ultra and Ultra 2.0 electronic humidifier. The cartridge clips on to the control unit and contains a foam element with the distilled water and antifungal agent. The water cartridge may be refilled once or twice, remember only with distilled water, but eventually the foam breaks down and holds less and will need more frequent refilling. Also with use the antifungal agent is depleted and eventually it is suggested that you replace the water cartridge with a new one.