How to distinguish between activated carbon system standards
When it comes to certifying activated carbon systems, there is some confusion about which standards best apply. Specifically, there may be some difficulty in distinguishing between the two American National Standards Institute (ANSI) standards covering drinking water treatment units: NSF/ANSI 42 and NSF/ANSI 53. Both of these standards cover products using activated carbon or carbon blocks as the primary technology to treat drinking water at the point of use (POU) or point of entry (POE). The main difference between these standards is that NSF/ANSI 42 addresses the aesthetic qualities of drinking water, while NSF/ANSI 53 addresses health effects. Products can achieve certification to either or both standards.
Before getting into the differences between NSF/ANSI 42: Drinking Water Treatment Units – Aesthetic Effects and NSF/ANSI 53: Drinking Water Treatment Units – Health Effects, we will look at their similarities.
Both standards establish minimum requirements for the materials, design and construction, and performance of drinking water treatment systems designed to reduce specific contaminants in public or private water supplies. Both standards also specify the minimum amount of information manufacturers must provide on product literature and labels for authorized representatives and system owners, as well as on service instructions for system owners. More details on the testing similarities are provided in Table 1.
The main difference between the standards is that NSF/ANSI 42 covers contaminant reduction claims solely related to aesthetic treatment of water, while NSF/ANSI 53 covers only claims of reduction of contaminants with health effects. In addition, while the level of complexity involved in testing any contaminant reduction claim varies based on the type of contaminant and type of claim, test methods for claims related to contaminants with health effects are especially rigorous and different from those required for aesthetic effects.
The main difference in testing for aesthetic versus health effects concerns contaminant reduction. While test pressure for POU and POE systems and on/off cycling requirements for POU systems are the same, there are several differences in contaminant reduction requirements between NSF/ANSI 42 and NSF/ANSI 53, as shown in Table 2.
The test methods differ between the two standards largely in that NSF/ANSI 53 has a more difficult or more protective test condition as it covers health effects protection for consumers. The NSF Joint Committee on Drinking Water Treatment Units, the group that developed and maintains both standards, is committed to the protection of public health. It demonstrated this commitment by developing an entire standard, NSF/ANSI 53, to spell out the conservative contaminant reduction test methods appropriate for claims of reduction of contaminants with health effects.
NSF/ANSI 42 (for aesthetic effects testing) 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 simulate 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. Even though NSF/ANSI 42 covers aesthetic effects, it includes a material safety evaluation and extraction testing.
The contaminant reduction test methods for NSF/ANSI 53 build on those of NSF/ANSI 42, but take the requirements to a higher level. The goal is to provide a high degree of confidence in the performance of systems that conform to NSF/ANSI 53. Some of the added criteria include that the end point of the test is double the manufacturer’s claimed capacity as required by NSF/ANSI 42 and that flow rate is not controlled by the laboratory. The more difficult test criteria help create higher confidence in conforming systems.
The similarities in many test requirements and other criteria in NSF/ANSI 42 and NSF/ANSI 53 create some unique considerations and opportunities to leverage test results when it comes to product certification.
Products can be certified to both NSF/ANSI 42 and NSF/ANSI 53 for manufacturers making both aesthetic and health claims. Even though the tests for each standard are extensive, a complete set of separate tests is not required for certification to both standards. Some tests can be used to satisfy the criteria of both standards, meaning that: