For IAS190S (2L ltr) purifier, 1 unit of IAC190S suffices as a replacement cartridge.
Higher capacity configurations of 4L or 6L ltrs require additional IAC190S cartridges. You may need to add appropriate # of 2L ltr capacity cartridges.
NOTE: 3M suggests to replace this cartridge(s) after full capacity of purification or 1 year, whichever is earlier
