It is recommended to replace the Cigar Oasis Cartridge approximately once a year as it becomes less absorbent with each refill. Use this water refill cartridge to replace the cartridge on the new Cigar Oasis Plus and original Cigar Oasis Plus and Cigar Oasis XL Plus models. Cigar Oasis refill cartridges that clip on to the control unit contain a foam element and anti-fungal agent. You must fill the cartridge with distilled water prior to first use. Typically, for a well-sealed humidor of 75-125 cigars that is opened 3-5 times a week, the water cartridge could last as long as 9-12 months. The water cartridge may be refilled with distilled water but should be replaced after 3 or 4 refills. This cartridge does not fit the Cigar Oasis Excel unit, a separate cartridge made specifically for this unit is sold separately. Dimensions: 6″ long x 2″ wide x 2.25″ high.