The Cold Forge does not include water filtration or disinfection, so it requires that you change the water regularly--about every 10 plunges seems to work for many Forgers.
The Filtered Forge includes water filtration and disinfection, so if your water is anything less than super crystal clear and beautiful, there's something wrong with your and it's probably our fault. Let us know and we'll fix it.
The Filtered Forge will require a new filter cartridge about once a year. You may also change the water every six month to avoid a build up of metal ions and salts in the water, because our treatment system will not remove these ions.