By Rick Andrew

Many people in the POU/POE industry have heard of NSF/ANSI42 and NSF/ANSI 53. These standards have been around for many years and there are a large number of products certified to them. A fair number of industry professionals further understand that these two standards cover activated carbon technology and that the majority of the products certified to them use activated carbon or carbon blocks as the primary treatment technology. What some folks don’t understand about these standards, though, is why there are two of them. After all, there is only one standard for POU water softeners: NSF/ANSI 44. And NSF/ANSI 58 is the only standard for POU RO systems. Ultraviolet systems are covered by one standard: NSF/ANSI 55. And the only standard for POU/POE distillation systems is NSF/ ANSI 62.

Two standards—one technology
The reason there are two standards for one technology is because of the complexity of testing for contaminant-reduction claims and also the desire to for highly rigorous test methods for claims related to contaminants with health effects. So, we therefore have two standards:

  1. NSF/ANSI 42–Drinking water treatment units–Aesthetic effects
  2. NSF/ANSI 53–Drinking water treatment units–Health effects

NSF/ANSI 42 covers all aspects of these products (material safety, structural integrity, general requirements, contaminant- reduction, product literature), although the contaminant- reduction claims are limited to claims of aesthetic treatment of the water. NSF/ANSI 53 is similar and parallel in terms of scope, except that the contaminant-reduction claims are limited to claims of reduction of contaminants with health effects. Given that the split in the standards is related to the contaminant- reduction claims, it is then logical that many elements of these two standards are identical or very similar. Essentially, the two standards parallel each other for all of the requirements except contaminant-reduction testing. A summary of these common elements is presented in Figure 1.

Increased rigor for health claims
NSF/ANSI 42 includes detailed methods and an overall conservative approach to requirements for claims of contaminant reduction. Plumbed-in systems are tested with a relatively high inlet pressure and POU systems are cycled on and off to simu- late consumer usage. The rate of cycling results in an accelerated usage pattern. Samples of the influent (contaminated) and product (treated) water are collected over the life of the product at various intervals, depending on the specific contaminant being tested, to assess performance on an ongoing basis.

The contaminant-reduction test methods under NSF/ANSI 53, however, build on those in NSF/ANSI 42, but take the requirements to a much higher level. The intent is to have a very high degree of confidence in the performance of systems that conform to NSF/ANSI 53. There are many aspects of the increased rigor, from the end point of the test to the fact that flowrate is not con- trolled by the laboratory, and much more. Figure 2 summarizes various criteria in the test methods under these standards and allows a comparison to demonstrate the ways in which NSF/ANSI 53 deviates from NSF/ANSI 42 in order to make the tests more difficult, creating exceptional confidence in conforming systems.

Basically, in each case where there is a difference in the test methods, the difference is such that NSF/ANSI 53 has a more difficult or more protective test condition. When all of these differences are considered together, the sum total is quite considerable in terms of establishing consumer protection.

Considerations for certification
As we have seen in Figure 1, there are many similarities in requirements between the two standards. These similarities in various test requirements and other criteria in NSF/ANSI 42 and NSF/ANSI 53 create some unique considerations and opportuni- ties to leverage test results when it comes to product certification.

Many products are certified to both NSF/ANSI 42 and NSF/ANSI 53 because the manufacturer makes both aesthetic and health claims on them.

  • One material safety evaluation, including one extraction test, is sufficient to certify a product to both standards.
  • One set of structural integrity tests is sufficient to certify a product to both standards.
  • One evaluation of general requirements is sufficient to certify a product to both standards, although evaluation of a performance indication device is not required if the certification will be only to NSF/ANSI 42.
  • Product literature that conforms to either standard will need only minor edits to conform to both standards, because most of the required statements for product literature are included in both.

Achieving clarity
Over the years, there have been various misconceptions related to NSF/ANSI 42 and NSF/ANSI 53. Some thought that because NSF/ANSI 42 included the words aesthetic effects in the title, that it did not include a material safety evaluation or extraction testing. Of course, it does. Others thought that the requirements for material safety were different between the two standards, leading to two extraction tests being required to certify a product to both standards. One extraction test, however, is sufficient to establish conformance to both. The difference in the two standards is related to the fact that the NSF Joint Committee on Drinking Water Treatment Units is committed to the protection of public health. They demonstrated their commitment by developing an entire standard, NSF/ANSI 53, specifically to spell out the conservative contaminant-reduction test methods that are appropriate for claims of reduction of contaminants with health effects.

About the author
Rick Andrew is the General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. He has previously served as the Operations Manager and, prior to that, Technical Manager for the program. 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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