By Rick Andrew
There are a wide variety of POU systems that utilize activated carbon in granular form or in carbon block form, either as the primary treatment technology in the system or as a secondary technology, such as a postfilter to a POU RO system. Considering the widespread use of activated carbon for POU systems, it only stands to reason that there are well established NSF/ANSI standards addressing POU activated carbon systems. These standards include:
- NSF/ANSI 42 – Drinking water treatment units – Aesthetic effects
- NSF/ANSI 53 – Drinking water treatment units – Health effects
- NSF/ANSI 401 – Drinking water treatment units – Emerging compounds / incidental contaminants
The term aesthetic effects in the context of NSF/ANSI 42 means that the contaminant reduction claims associated with that standard are related to aesthetic water treatment: taste, odor and appearance. Conversely, claims of treatment of contaminants with documented health effects at concentrations that have been found in source water and drinking water are included under NSF/ANSI 53.
NSF/ANSI 401 provides yet a third category of contaminant reduction claims: emerging compounds and incidental contaminants. These are trace compounds detected in drinking water or source water but not at levels that are documented to cause health effects or to be noticeable in terms of taste, odor or appearance of the water. Nonetheless, consumers would prefer to be able to reduce the levels of these contaminants as low as possible.
POU products making claims of aesthetic treatment and of treatment of health-related contaminants often conform to both NSF/ANSI 42 and NSF/ANSI 53. Some products have associated claims under and conform to all three standards. This idea of products conforming to multiple standards and having multiple standards for the same products can cause confusion; however, the key to sorting out this confusion is to consider the similarities and differences among the standards.
Requirements under the standards
These standards include criteria and test methodologies for evaluation of several critical aspects of POU activated carbon systems, including:
- Safety of materials in contact with drinking water
- Structural integrity for products connected to a pressurized water supply
- General requirements for flowrate, etc.
- Contaminant reduction
- Product literature (user information) including data plate, performance data sheet, replacement element packaging and installation and operation instructions
The three 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 material safety de facto conforms to NSF/ANSI 53 and NSF/ANSI 401 for the same requirements.
There is also substantial alignment for general requirements and product literature among the three standards, although the requirements are not identical. The differences arise because of specific aspects of the products or the requirements that may vary depending on whether the treatment is aesthetic or is related to health claims or claims of reduction of emerging compounds or incidental contaminants.
For example, NSF/ANSI 53 and NSF/ANSI 401 include requirements for performance indication devices (PIDs) that inform users when replaceable treatment elements are due to be changed. Because NSF/ANSI 42 is addressing only aesthetic treatment of the water, however, there are no requirements for PIDs in NSF/ANSI 42. Other general requirements spelled out under the three standards include prohibitions on sharp edges that could cause injury, criteria for ease in changing of replacement filters, minimum acceptable flowrates and some other miscellaneous requirements.
Product literature requirements that spell out user responsibilities are also quite similar under the three standards. These requirements address system data plates, installation and operation instructions, performance data sheets and replacement element packaging. All are addressed by specifying 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.
Test methods for contaminant reduction
In contrast to other sections of the standards, the requirements for contaminant reduction testing do have some significant variation among the three standards. Although there are many 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 into three different standards instead of including all of the requirements in a single standard. Figure 1 demonstrates a comparison of the three standards contaminant reduction test method criteria across several different critical parameters, highlighting the similarities and differences in approach among them.
NSF/ANSI 53 is generally more conservative (more difficult) than NSF/ANSI 42 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. 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. NSF/ANSI 401 tracks more similarly to NSF/ANSI 53 but the basis for influent and maximum product water concentrations is not based on health effects because the compounds in NSF/ANSI 401 don’t include health effects at the levels at which they are being detected in source water and/or drinking water.
Conformance to all three standards
It is quite common for POU activated carbon filter systems to conform to NSF/ANSI 42 and NSF/ANSI 53, and sometimes to all three standards. The significant overlap in the criteria facilitate conformance to all three. One extraction test for safety of materials in contact with drinking water and one set of structural integrity tests address these requirements under all three. 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 all three standards. Evaluation of the PID, if applicable, according to NSF/ANSI 53 addresses that requirement for both NSF/ANSI 53 and NSF/ANSI 401. Although most product literature requirements are similar under all three standards, there must be assurance that all applicable requirements are included in the installation and operation instructions, on the system data plate, in the performance data sheet and on the replacement element packaging. Finally, testing for contaminant reduction performance according to the requirements of the applicable standard for each claim made by the manufacturer establishes system conformance to all three standards.
The concept of having three standards applicable to the same products can sometimes cause confusion. Keeping in mind the overlap in the standards (and those aspects of the systems that have identical or similar requirements under all three standards) definitely helps with understanding. Similarly, remembering the differences in contaminant reduction testing and the greater robustness (more conservatism) associated with contaminant reduction testing under NSF/ANSI 53 (and not having regulated levels as a basis for contaminant reduction testing under NSF/ANSI 401) rounds out understanding of the similarities and differences among the three standards. All of this understanding makes it clear why so many products conform to NSF/ANSI 42 and NSF/ANSI 53 and some to all three 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: Andrew@nsf.org