By Rick Andrew

Activated carbon is one of the most widely used technologies in POU treatment. There are many POU systems that utilize activated carbon in granular form or in carbon block form either as the primary treatment technology in the system or secondary technology, such as a postfilter to a POU RO system. Considering the widespread use of activated carbon, it is no surprise that there are well-established NSF/ANSI standards addressing POU activated carbon systems. These standards are NSF/ANSI 42–Drinking water treatment units–Aesthetic effects and NSF/ANSI 53–Drinking water treatment units–Health effects.

The term aesthetic effects in context of NSF/ANSI 42 is not meant to imply that the standard does not address any health effects issues associated with POU filters, because it actually does in terms of any contaminants that may potentially leach or extract from the filter. Rather, this term is related to the type of contaminant reduction claims associated with the POU systems conforming to NSF/ANSI 42. Claims of aesthetic water treatment are addressed under NSF/ANSI 42. Conversely, claims for treatment of health-related contaminants that may be present in drinking water are included under NSF/ANSI 53. POU products making claims for aesthetic treatment and claims for treatment of health related contaminants often conform to both NSF/ANSI 42 and 53. This idea of products conforming to two standards, and having two standards for the same products, can cause confusion. The key to sorting out this confusion, however, is to consider the similarities and differences between the standards.

Evaluation criteria
These standards include criteria and test methodologies for evaluation of several critical aspects of POU activated carbon systems, including:

  • Safety for contact with drinking water
  • Structural integrity
  • General requirements
  • Contaminant reduction
  • Product literature (user information)

The two standards are well aligned in terms of requirements for safety for contact with drinking water and structural integrity. In fact, the requirements are identical, such that a POU filter conforming to NSF/ANSI 42 for these requirements de facto conforms to NSF/ANSI 53 for the same requirements.

There is also alignment for general requirements and product literature between the two standards, although the requirements are not identical. The differences arise due to specific aspects of the products that may vary depending on whether the treatment is aesthetic or is related to health claims. For example, NSF/ANSI 53 includes requirements for performance indication devices (PIDs) that inform users when replaceable treatment elements are due to be changed. Because NSF/ANSI 42 is dealing strictly with aesthetic treatment of the water, however, there are no requirements for PIDs in that standard.

Other general requirements spelled out under NSF/ANSI 42 and 53 include prohibitions on sharp edges that could cause injury, criteria for ease in changing of replacement filters, minimum acceptable flowrates and a few other similar miscellaneous-type requirements. User information in the form of product literature requirements are also quite similar under these standards in that system data plates, installation and operation instructions, performance data sheets and replacement element packaging are all addressed by detailing out specific information that must be included. There are a few differences in these requirements due to the differences in the types of contaminant reduction claims under the standards. For example, NSF/ANSI 53 includes requirements for detailed information for systems making arsenic reduction claims, to help users clearly understand system capabilities and limitations.

Contaminant reduction performance
There is one section of these two standards that does have significant differences: criteria for contaminant reduction claims. Although there are some basic similarities, such as the concept of checking performance at multiple points throughout the test as opposed to only at the end, there are also some fundamental differences. It is these fundamental differences that form the rationale for separating NSF/ANSI 42 and 53 into two different standards instead of combining them into one. Figure 1 shows a comparison of NSF/ANSI 42 and 53 contaminant reduction claims criteria across several different critical parameters, demonstrating the similarities and differences in approach. In general, NSF/ANSI 53 is more conservative (more difficult) because the contaminant reduction claims have health effects associated with them. Manufacturers and consumers are better protected by a more rigorous standard that sets a high bar for claims of reduction of contaminants that have health effects associated with them. And this higher level of conservatism in NSF/ANSI 53 is demonstrated across multiple parameters within the test method requirements: flowrate, end point, contaminant concentration in the challenge water and required reduction of the contaminant.

Conformance to both standards
It is quite common for POU activated carbon filter systems to conform to both NSF/ANSI 42 and 53. The significant overlap in the criteria facilitate conformance to both standards. One extraction test for safety of materials in contact with drinking water and one set of structural integrity tests address these requirements under both standards. One evaluation of the minimum service flowrate, the ease of changing of replacement filters and for sharp edges likely to cause injury addresses requirements in both standards. Evaluation of the PID (if applicable, according to NSF/ANSI 53) addresses that requirement. There must be assurance that all applicable requirements for product literature under both standards are included in the installation and operation instructions, on the system data plate, in the performance data sheet and on the replacement element packaging. And then testing for contaminant reduction performance according to the requirements of the applicable standard for each claim made by the manufacturer establishes system conformance to both NSF/ANSI 42 and 53.

Two standards for the same products
This concept of having two standards applicable to the same products can sometimes cause confusion. Keeping in mind the overlap in the two standards, and those aspects of the systems that have identical or similar requirements under both standards, definitely helps with understanding. Keeping in mind the differences in contaminant reduction testing, and the greater robustness (more conservatism) associated with contaminant reduction testing under NSF/ANSI 53, rounds out understanding of the similarities and differences between these two standards. All of this understanding makes it clear why so many products conform to both standards.

About the author

Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: [email protected]


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