Ezifit Water Filter Cartridges are in their own heavy duty pressure housing. Every time the filter is replaced, the housing is automatically renewed. No need to sanitise old housing, no mess, no risk of leaking and no orings to change. ** ezifit replacement filters are rigorously performance tested by a NATA certified laboratory at the AWQC approved and comply to AUS/ NZ4348:1995 standards. All components are also Tested and certified to Australian Standard AS3497, NSF certified replacement cartridges. Available in twin filter, triple filter and 4 stage ultrafine packs.