By Rick Andrew
The NSF/ANSI DWTU Standards for POU/POE drinking water treatment products require that material safety of products for contact with drinking water be established. This requirement assures that consumers seeking to improve the quality of their drinking water through the use of POU and/or POE systems do not inadvertently make it worse by using products that leach contaminants into the drinking water.
The way this requirement is structured is through a four-step process. The requirements for each step are described in detail in Section 4 of the NSF/ANSI DWTU Standards. In general terms, the steps can be described as follows:
- Determine which contaminants might potentially leach into drinking water from the product by reviewing the materials that are in contact with drinking water.
- Expose the product to water under specific conditions and collect appropriate samples of this water after it has been exposed to the product.
- Analyze the water for the contaminants identified in Step 1 to see which contaminants, if any, leached into the water in Step 2.
- Assess the concentration(s) of any contaminants detected in Step 3 to assess toxicological risk and conformance to the requirements of the Standard. Any contaminants detected above acceptable risk-based concentrations result in a test failure.
Testing with and without media
An interesting nuance to this process is that products that contain adsorptive or absorptive media, e.g. activated carbon, must be tested with and without the media. All four steps of the process are completed both for the product as sold (with the media), and then for same product without the media. The language for this requirement appears in Section 4.2.3.5 of NSF/ANSI 42 and 53, and in similar sections of the other NSF/ANSI DWTU Standards:
“4.2.3.5 Systems with adsorptive or absorptive media shall be tested with and without the media. Testing without media shall include removal of any granular adsorptive or absorptive media, and removal of any adsorptive or absorptive replacement elements.”
The rationale
The reason for testing with the media is more obvious – this is the product as it is sold. It only makes sense to evaluate the product for material safety in the configuration in which it is sold. Less obvious is the rationale for testing without the media. There are actually two reasons behind this requirement. These reasons both begin with the issue that the media could potentially adsorb contaminants leaching from other materials used in construction of the product and in contact with drinking water. The first reason, based on this issue, is that because the exposure of the product to water in Step 2 (above) is for a short duration, the extraction testing protocol does not evaluate the ability of the media to continue to adsorb contaminants throughout the life of the product.
The second reason is that consumers may opt to use the product without the media. In this case, contaminants leaching from the non-media parts of the product would not be treated by the media at all. The best example is when a consumer experiences a clogged filter and for some reason does not immediately replace it, but rather simply removes the filter and continues to use the water by simply running it through an empty filter housing.
Practical issues related to without-media testing
Testing a product in the form as sold is typically pretty straightforward. If it is a complete system, the product is designed to flow drinking water through it. When removing media, however, there are practical considerations and challenges when considering exactly which parts are considered to be media and how to effectively test the product with these parts removed. Questions such as the following come to mind:
- What about the plastic binder materials used to make carbon blocks – are these materials considered to be media? If not, how can they be included in a test sample without the media?
- What about end caps, glues, gaskets and media wraps used on carbon filter replacement elements? Should these be tested without the media? If so, how?
- What about encapsulated-type filter cartridges (quarter-turn, quick-change, etc.) containing carbon filters? How are these tested?
- What about RO elements? Are they considered to be media?
These questions are addressed by the Standard; for example, refer to the second sentence of NSF/ANSI 42 and 53 Section 4.2.3.5:
“4.2.3.5 Systems with adsorptive or absorptive media shall be tested with and without the media. Testing without media shall include removal of any granular adsorptive or absorptive media, and removal of any adsorptive or absorptive replacement elements.”
It makes clear that plastic binder materials need not be tested in without-media extraction testing because the Standard indicates that the whole replacement element is to be removed for this testing. The same is true of end caps, glues, gaskets and media wraps. Encapsulated filter cartridges can be a bit trickier. According to the Standard, they are to be removed, however, the product may no longer be watertight when the cartridge is removed. Some type of adjustment must be made to allow the exposure for the testing if the product is not watertight with the cartridge removed. Common options here are for the manufacturer to make special test units that include filter cartridges without the carbon filter inside the cartridge housing, or for the manufacturer to supply a bypass plug to allow the product to be watertight without the filter cartridge in place. And finally, RO elements are not considered to be adsorptive or adsorptive because this is not their primary treatment function. Figure 1 describes some common types of products and how they are tested for extraction with and without media under the requirements of the NSF/ANSI DWTU Standards.
Details and nuances in the Standards help assure safer products
It is clear from exploring the details and rationales in discussions such as this one that a great deal of thought and consideration has been put into development of the requirements of the NSF/ANSI DWTU Standards. The NSF Joint Committee on Drinking Water Treatment Units has a great history of thoughtful and scientific assessment of products, risks and possible failure modes that have led to the comprehensive Standards that we benefit from today. And far from being static documents, these Standards are continually developed and refined as the Joint Committee fulfills its ongoing mission to produce the best possible standards to help assure the safety of today’s POU/POE equipment.
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 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].