Manufacturers of carbon filters, replacement filters and similar products have them tested only against the material extraction requirements of the standard. As a result, component manufacturers cannot make any type of performance claim related to the removal of chlorine or lead. Manufacturers of pressure-bearing components are also evaluated against the structural integrity requirements of the standard. When these components are sold to manufacturers of a complete system, they know that the components already meet the standard's material extraction requirements and, when applicable, structural integrity requirements. This saves time and reduces the cost of system certification.
Different technologies have different filtration capabilities.
Many systems are hybrids of different filtration technologies, potentially enabling them to remove a wider range of contaminants from the water. Occasionally a noncertified system using a Certified component will claim that it is a NSF Certified system. This is not so. Simply using all NSF Certified materials or using an NSF Certified filter in a system does not mean that the system can bear the NSF Mark. To display the NSF Mark, the entire system must go through the certification process.