Filtering Your Options

March 22, 2019

Everything you need to know about the testing & certification of microbiological purifiers to NSF P231

About the author:

Jason Carlson is staff chemist, water systems for UL LLC. Carlson can be reached at [email protected] or 847.664.3179.

A report published in the medical journal The Lancet concluded that the lack of safe drinking water and proper sanitation take a greater toll on human life globally than war, terrorism and potential weapons of mass destruction combined. The World Health Organization (WHO) states that every year more than 3.4 million people die as a result of water-related diseases, making it the leading cause of disease and death around the world. Of these, 1.8 million deaths are caused by diarrheal diseases, and for children under five years of age, this burden is greater than HIV and malaria combined. 

The 71% of the world’s population lucky enough to have access to a safely managed water service often take it for granted. We do not think about how easy it is to obtain a clean glass of water for ourselves and our families. How would you produce that same glass of water if you were not connected to a safe distribution system, either by choice or due to an unforeseen event? For individuals using an alternative water source, such as a private subsurface or surface water reservoir on rural property, delivered water held in cisterns, or harvested rain water, this also is an important question. For those dependent on managed water systems, how would you provide safe drinking water if you suddenly were cut off from your water main due to a simple line break or even an earthquake, tsunami, wildfire, or other natural or manmade disaster? What about those traveling to remote parts of the world or venturing off on a backcountry camping trip? How do they produce consistently safe water?

This article will describe some of the common microbiological water concerns and the technologies that exist for eliminating them. This does not cover the removal of organic or inorganic chemicals or radiological contaminants that also could be present and pose risks in potential drinking water sources. It will discuss an existing NSF test protocol and third-party certification option called NSF P231 offered by UL. Finally, the article will explain the difference between testing to and being certified to these standards, and how current product claims in the market may be misleading. 

Contaminants & Risks

When it comes to microbiological contaminants in drinking water, there are three major types: protozoa, bacteria and virus. Each of these require different levels of filtration or alternate treatment techniques. All three typically enter water sources as a result of contamination with human or animal waste. 

The first type of microorganism that can cause issues with human health are protozoa. Examples of protozoan that could lead to infection are Amoebae, Cryptosporidia and Giardia. Protozoa are the easiest microorganism to remove with mechanical filtration and can be removed by filters with absolute pore sizes of 1 µ (1⁄1000 of a millimeter) or smaller. Some protozoa, such as Cryptosporidia, can enter a protected dormant state when unfavorable conditions exist, forming a hard outer shell and becoming a cyst. 

The next organism of concern is bacteria. These are smaller cells in the order of 0.2 µ to a few microns in diameter. Examples of disease causing species found in potential drinking water sources are Campylobacter, E.coli, Salmonella and Vibrio cholerae. Infections caused by bacteria in drinking water can range from gastrointestinal discomfort to life-threatening illness. Bacteria can be removed mechanically with filtration units with absolute pore sizes smaller than 0.2 µ. 

Finally, viruses are the smallest and most difficult organisms to remove from a contaminated drinking water source. A virus contains little more than short DNA or RNA segments protected by an outer protein shell. They do not reproduce on their own nor have any internal metabolic processes. Examples of viruses that can be found in contaminated drinking water sources are rotovirus, norovirus and Hepatitis A. Due to their small size, down to 0.02 µ, few filters on the market can remove them mechanically. Typically a secondary chemical or ultraviolet (UV) treatment is required to destroy or inactivate viruses. 

Most small personal-use filtration units on the market for reducing microbiologicals rely on hollow fiber, ceramic element or glass fiber microfiltration. These products rely on pore sizes in 0.1 to 0.2 µ range to mechanically remove protozoa and bacteria from the water source. These filters typically report reductions of 99.9999% (6 Log) or greater for bacteria and 99.9% (3 Log) or greater for cysts/protozoa. However, these are not the only technologies available. Personal use treatment options using chlorine dioxide tablets or ultraviolet emission are available as primary or secondary treatments. To be considered a true water purifier, a device or system must remove, inactivate or destroy all disease-causing microorganisms. In addition to the protozoa and bacteria claims above, a device also would need to reduce viruses by 99.99% (4 Log).  

Certifications & Claims

What standardized test methods, requirements, or certifications exist for a manufacturer to substantiate microbiological reduction claims or a customer to make an informed purchasing decision? The remainder of this article will focus on NSF P231, which covers drinking water treatment units with flow rates less than 5 gal per minute (gpm) that are intended to treat water of unknown microbiological quality but presumed to be potable. For reference, a household faucet typically has a flow rate of 2.2 gpm or less. 

Applications of P231 type filters include use after floods and natural disasters; contaminated individual sources, such as wells and springs, motorhomes and trailers; foreign travel; and use while backpacking or camping. It should be noted that these types of systems are not intended to convert wastewater or sewage into drinking water. The purpose of this protocol is to establish minimum requirements for health and sanitation characteristics.

 The NSF P231 protocol document is intertwined with the U.S. EPA’s Task Force Report, Guide Standard and Protocol for Testing Microbiological Water Purifiers. In fact, the EPA Guide Standard is provided in its entirety as P231 Annex B. What NSF P231 adds is clarity on how to evaluate the health effects of materials used to build the units; the design, construction and structural integrity; reduction performance; product literature requirements and certifier audit; and periodic retest criteria.  

For material health effects, construction and structural integrity, P231 defers to a product needing to meet the requirements laid out within other published NSF drinking water treatment unit standards, such as NSF 53 health effects, NSF 55 UV treatment units, NSF 58 reverse osmosis units, or NSF 62 distillation systems. If the technology evaluated under the scope of P231 does not fall under one of the established standards, an equivalent evaluation method with equivalent criteria shall be used.  

The reduction claim performance for protozoa, bacteria and viruses contained in NSF P231 are directly from the EPA guide standard. Representative test organisms or organism surrogates are referenced for challenge studies along with the minimum requirements for 3 Log, 4 Log, or 6 Log reductions for cysts, viruses, and bacteria respectively. These Log reductions are based on EPA studies that determined worst-case environmental concentrations for contaminated streams and other bodies of water. Section 3 of the EPA Guide Standard goes into greater detail on how to perform the reduction testing, construct the test apparatus or rig and, in addition to the microbiological challenges, how to formulate various challenge waters based on the reduction technology used. 

Decoding Claims

Let us now look at the difference between third-party certification to NSF P231 versus claims that a product meets or exceeds P231 or the EPA Guide Standard. A quick online product search or visit to a hardware or sporting goods store to read product packaging will reveal multiple claims such as “meets or exceeds NSF and EPA protocols and guidelines,” “EPA approved,” or “Meets NSF protocol P231 for removal of bacteria (99.9999%) and protozoa (99.9%)” to give a few examples.

Any product claiming that it is EPA approved is a misleading claim. The EPA does not certify, approve or maintain a database of specific purifier manufacturers or approved products. Products claiming to meet or exceed NSF and/or EPA protocols, or specifically meet or exceed P231, also are using misleading statements. The product may in fact meet or exceed a reduction claim, such as for bacteria and protozoa, but this does not mean it also meets the virus-reduction claims. For a product to truly be a water purifier, it must eliminate all types of microorganisms, including viruses. A product does not meet the performance requirements of NSF P231 or the EPA Guide Standard unless it meets all three of the organism reduction requirements. 

Additionally, saying a product is compliant to or meets NSF requirements while not being certified does not clarify whether the product was evaluated for material safety and structural integrity, or only evaluated to certain requirements the manufacturer deemed relevant. A product actually certified by an unbiased third party, such as UL, would not only be evaluated to all P231 reduction requirements, but also would be subject to annual inspections of the manufacturing facilities, and audits and evaluations of new materials and suppliers for potential toxicological risks. Products would be retested for reduction claims when substantial design and material changes occur or, at the very least, tested every five years when changes did not occur. When a product is not certified, there is no assurance that there has not been a substantial lapse in time or change to product design prior to claims being made.

Microbiological contamination of potential drinking water sources is a serious health concern worldwide. Even in areas where safe water typically is available, circumstances may arise that require an individual to use a purification device to minimize their risk of exposure to disease-causing organisms. Fortunately, there are devices on the market that may protect you from all or some of these risks. NSF protocol P231 certification by a third party can help manufacturers substantiate a product’s reduction claims and overall safety. Products that are not certified but claim to be compliant with some of the P231 or EPA Guide Standard requirements may mislead customers as to what actually was evaluated. Full NSF P231 certification helps eliminate this uncertainty for buyers and sets manufacturers apart from the competition. 

About the Author

Jason Carlson

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