Thank you for viewing. All four are brand new and unopened. I have been purchasing these regularly from the management company of my current rental apartment, but I will be moving soon, so I am offering them to someone who needs them. SANEI water purifier cartridge M71750M-1, set of 4, compatible with Column Series water purifiers. - Model: M71750M-1 - Type: Water purifier cartridge - Quantity: Set of 4 - Applicable models: For Column Series water purifiers - Brand: SANEI