By Rick Andrew and Theresa Bellish

In addition to detailing requirements for conformity assessment for complete drinking water treatment unit systems, the NSF/ANSI DWTU Standards include requirements for the evaluation of components of those units. Manufacturers of these components have the ability to assess whether the components will be suitable for complete system manufacturers, who wish to assemble or manufacture systems that conform to the standards. By seeking components that have been evaluated to the standards, system manufacturers can reduce the risks of test failures or other conformance issues associated with purchased components.

There are many different components that can be evaluated, including filter housings, filter cartridges, membrane elements, media tanks, media and many more. These types of components, in certain size ranges, are mainly used for POU/POE applications. Typically there is not much doubt for the manufacturer of these components as to which NSF/ANSI standards are applicable or are the most relevant.

Other types of components, however, can be used in manufacturing of POU/POE systems, but can also have numerous other end uses. Some of these fall under the scope of other standards, even other NSF/ANSI standards. These various end uses (some covered under different standards) can create confusion for both the component manufacturers and also for POU/POE system manufacturers that are using these components. This confusion can particularly arise with regard to tubing and O-rings. Here we will examine some of the common end uses and associated standards to help bring some clarity to what can be a cloudy view.

End uses influence standard requirements
On the surface, it may seem strange that the same product could have different standard requirements based on the end use. Why not just have one standard for a given product and be done with it? While the simplicity of that approach is appealing, the reality is that there can be very significant differences in end uses that require different properties and characteristics in the products. For example, consider a large pipe or valve or coating used in a main line of a public water distribution system. The water in contact with these products and materials is flowing continually or nearly continually, with a relatively brief contact time. In contrast, the water in a POU filter or RO system may dwell in that system for long periods of time between uses of the system, including overnight periods.

Or consider a material used in a food-contact environment as opposed to drinking water. These materials may be in contact with liquids other than water, such as juices or dairy products. Additionally, cleaning and sanitation of equipment is critical in the world of food safety in restaurants. All of these various differences in end use lead to differences in the desired characteristics of materials and components. And those differences lead to different standard requirements.

Standards and end uses
When it comes to tubing and O-rings, there are really four primary NSF/ANSI standards that could apply based on the specific intended end use. These standards, their titles and scopes are briefly described in Figure 1. Faced with consideration of four different standards, it seems that there could be a dilemma faced by manufacturers of tubing and O-rings. What are they to do? The answer is based on their target markets. If they are selling primarily for drinking water contact end use, other than POU, then they should consider NSF/ANSI 61 for conformity assessment. If they are focused on the commercial food equipment market, then NSF/ANSI 51 is the most important standard.

So what if these manufacturers are primarily interested in the POU market? There are two standards covering this market: NSF/ANSI 42 and NSF/ANSI 58. There are two different standards because of the differences in contaminant-reduction testing methodology for filter systems versus POU RO systems. For tubing and O-ring components, the requirements in NSF/ANSI 42 and NSF/ANSI 58 are essentially the same. The tubing and O-ring manufacturers can evaluate conformance to both of them under basically identical criteria.

From the POU system manufacturer perspective
While the existence of multiple standards applying to tubing and O-rings can create confusion for those manufacturers, so too can it create confusion for POU system manufacturers. They may be considering purchasing components evaluated to a standard, but to a different standard from the one to which their systems are evaluated. What does this mean for the POU system manufacturer? The good news is that the components have been evaluated to a standard. This evaluation requires consistency in the manufacturing process, quality-control procedures and the evaluation itself. This underlying foundation of a quality manufacturing process is beneficial to any buyer of the product. The bad news, though, is that the requirements don’t exactly align. While the component is a quality product, the specific quality metrics associated with the specific standard for the POU system have not been applied to the component; it is an unknown as to how that component will fare when evaluated in a POU system.

Conformance to multiple standards
Given this reality, some component manufacturers who sell to various end-use markets evaluate conformance of their components to multiple standards. The requirements of these standards are not mutually exclusive and in fact, it is possible to manufacture tubing and O-rings that meet the requirements of all four of the standards being discussed here. Maintaining conformance to multiple standards requires sophisticated knowledge and understanding on the part of the component manufacturer and a serious commitment to quality. The reward, however, is access to multiple end-use markets with a very high degree of customer confidence.

Logic prevails
The landscape of quality standards is a complex one that can often be confusing. The idea that there are multiple standards applying to the same product is one that understandably leads to confusion in the absence of education and understanding. Fortunately, there is an underlying structure to the landscape, even a structure based on logic. Hopefully this explanation of that logic is helpful to both component suppliers and POU system manufacturers surveying this landscape of various standards for these components.

About the authors
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/), 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:

Theresa Bellish is NSF’s General Manager, Municipal and Recreational Water Programs. Previously, she served as Operations Manager of NSF’s Municipal Drinking Water Products, Public Drinking Water Equipment and Recreational Water Product Programs. Bellish has a Bachelor of Science Degree in nutrition and food science from Wayne State University. She can be reached at (800) NSF-MARK or email:


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