Cigar Oasis Water Cartridges that clip on to the control unit contains a foam element with the distilled water and antifungal agent. The fan in the Control Unit draws air from inside the humidor and passes the air through the foam which is full of water and the air picks up humidity and delivers it to the cigars in the humidor. Water consumption depends on the size of the humidor, how good the humidor seal is and how dry are the cigars when you put them in the humidor. 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 to 12 months.