NSF 42, 53, 58, 401 & More: Water Filter Certifications Explained

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If you’ve been browsing water filters recently, you’ve probably come across an NSF certification or two.

Many water treatment systems on today’s market are certified by the NSF or ANSI – and this certification is marketed as one of the filter’s biggest selling points.

But what does the NSF certification mean? How do manufacturers get their products certified? And is it worth buying a filter that doesn’t have a certification? I’ve covered all this and more in this NSF certifications guide.

๐Ÿšฐ Drinking Water System Standards in the United States

There are a number of independent bodies that have set standards for drinking water systems in the US. The standards you are most likely to hear about are as follows:

The Safe Drinking Water Act (SDWA)

The Safe Drinking Water Act was introduced by the US Environmental Protection Agency (EPA). This federal law was established in 1974, and is intended to ensure that public drinking water is safe and free from harmful or dangerous contaminants.

Every public water system in America must adhere to the SDWA. This act doesn’t cover private wells, and nor does it apply to bottled water.

American National Standards Institute (ANSI)

The American National Standards Institute, or ANSI for short, offers accreditation to companies that manufacture a broad range of products, including water filters.

To become ANSI accredited, a manufacturer must successfully complete an application process, and must be able to demonstrate that “their procedures for voluntary consensus standards development adhere to ANSI’s requirements and oversight”.

NSF International (NSFยฎ)

NSF International is an independent organization that has developed standards and certifications to protect water, food, consumer products, and the environment. The main purpose of NSF is to protect and improve human health on a global scale.

When a product is certified by NSF, it’ll have the NSF mark, which assures consumers that the product has been tested independently and deemed effective for public use.

If you read that a filter system is certified to both NSF and ANSI standards, that’s because NSF is an ANSI-accredited body, and these organizations often collaborate on producing new drinking water standards.

NSF Certified Drinking Water Treatment Units (DWTU)

Manufacturers of water filters have the option to apply to join NSF’s catalog of certified drinking water treatment units. To be featured in this catalog, water filters must adhere to NSF’s requirements for whatever standard they aim to be certified for.

From a customer perspective, having access to a catalog of certified products is incredibly handy. If you can’t find information about an NSF certification in a product’s marketing materials, you can simply search for it on the NSF DWTU list. You can also filter your search to focus on a specific certification or product type.

๐Ÿ“ NSF Standards for Drinking Water Treatment Systems

There are 13 NSF standards in place for drinking water treatment systems today. You might come across any of the following standards when searching for a water filter in the US:

nsf logo


NSF/ ANSI standard 42 is one of the most commonly available NSF standards today. Companies seeking an NSF 42 certification must be able to prove that their filter can greatly reduce or remove aesthetic contaminants, including chlorine (taste and odor) and chloramines.

Note that a filter won’t need to reduce or remove both chlorine and chloramines in order to be NSF certified.

You might read a filter that’s advertised to be “certified to NSF standard 42 for chlorine reduction”. In that case, you know that the filter offers an expected level of performance when it comes to reducing chlorine, but that doesn’t mean it can remove chloramines.

Refrigerator water filters and water pitcher filters are examples of products that are only certified to NSF/ANSI standard 42.


NSF 44 offers requirements for cation exchange water softeners that remove hardness minerals from public and private water supplies. Any system that uses a resin that requires regenerating with sodium or potassium chloride can apply for an NSF 44 certification.

A system will be required to meet a number of requirements to be NSF certified to standard 44. The scope of this certification includes structural integrity, material safety, reduction of hardness contaminants, accuracy of brine solution, rinse effectiveness, softening capacity, and accuracy of information provided to the user.


NSF/ANSI standard 53 is another common certification, and is awarded to filters that can remove specific contaminants that are known to cause health effects.

Typically, the filters that receive an NSF 53 certification don’t offer set contaminant reduction. The quality of the filter will affect performance, so don’t assume that all NSF 53 certified filters can remove the same types of contaminants, to the same effectiveness.

All companies should provide a performance data sheet for their water filters. This sheet should indicate exactly which contaminants the filter is certified to remove.

Some of the contaminants that NSF/ ANSI standard 53 covers are certain heavy metals (including lead, mercury, and arsenic), bacteria like Giardia and Cryptosporidium, herbicides and pesticides, benzene, radon, PCBs, MTBE, and trihalomethanes.

An NSF 53 certified carbon block filter can be used alone or as part of a reverse osmosis filter system (which has its own NSF certification, 58) to remove a broader range of contaminants.

Most products certified to NSF/ANSI standard 53 are under-sink systems. There are also a number of faucet-mount water filters that are NSF/ ANSI standard 53 certified.


NSF/ ANSI standard 55 applies to UV-LED technology that can kill microorganisms in drinking water.

This standard covers treatment systems that use ultraviolet (UV) light to kill viruses, cysts, mold and bacteria by inactivating them. These systems may be used to treat water that’s microbiologically unsafe, or disinfected tap water.

NSF 55 was developed in 1991, and originally applied to low-pressure UV systems using mercury – a technology that is now outdated. In 2019, the standard was finally revised to become more relevant to the UV-LED systems that are more commonly available today.

To gain an NSF standard 55 certification, a UV system should be capable of delivering a 40mJ (megajoules) dose of UV to water flowing through the system. This dosage is considered effective enough to kill at least 99.99% of pathogens in drinking water.


If you’re considering a reverse osmosis water filter, finding a system with an NSF 58 certification will give you peace of mind that its performance is up to standard.

If a system has an NSF 58 certification, it can remove much more than a typical filter can. Being certified to NSF/ ANSI 58 means that a system can remove the likes of nitrate and nitrite, heavy metals like lead, copper, mercury and chromium, fluoride, perchlorate, and much more.

Reverse osmosis filters are usually also certified to NSF 53, because a carbon block or activated carbon filter is involved in the RO process.

The overall performance of a reverse osmosis system depends on the quality of the RO membrane, as well as the carbon filter, pre-filter and post-filter that are used in the system. Again, consult the performance data sheet if you need additional information about what a reverse osmosis system can reduce.


NSF/ ANSI standard 62 applies to drinking water distiller systems. This standard establishes minimum requirements for construction, design, performance and materials for a distillation machine.

If a distiller is certified to NSF International 62, it has been proven to remove specific microbiological and chemical contaminants, including chlorine, bacteria, cysts, and viruses.

Distiller companies don’t have to prove that their product is capable of removing every one of these contaminants to obtain an NSF 62 certification. A system will have to simply remove one or more of the listed contaminants.

Distillers certified to NSCF 62 are intended for treatment of private well water or chlorinated water; not turbid water or water that has been obviously contaminated, such as raw sewage.


Chlorine-reducing showerhead water filters can apply for an NSF/ANSI 177 certification.

These filters offer aesthetic improvements to water, and an NSF 177 certification can verify performance claims and offer peace of mind to the customer that the filter has been deemed effective by an independent third party.

Shower filters should meet the NSF’s minimal certification requirements for showerhead applications, including structural integrity, material safety, minimum flow rate, free chlorine removal, and information provided to the user.

Note that NSF/ANSI 177 only applies to complete showerhead water filters. If a component or system offers features that are more applicable to other NSF standards, these will be certified accordingly.


NSF/ANSI 244 is a residential drinking water standard that applies to water filters that are used to protect against accidental microbiological contamination of private and public drinking water.

There are a number of water filter types that can be accredited by this certification: microfiltration, nanofiltration, ultrafiltration, ceramic filtration, and reverse osmosis treatment.

Systems will be tested for material safety, structural integrity and bacteria and virus reduction in order to receive an NSF 244 certification.


NSF/ ANSI standard 401 is one of the more recently established NSF standards, and is intended for water filters that can remove emerging compounds or incidental contaminants.

This standard was introduced when public water users became concerned about the trace pharmaceuticals that were making it into their tap water.

A filter with an NSF 401 certification may remove or reduce up to 15 kinds of emerging impurities, such as flame retardants, prescription drugs, detergents, and certain herbicides and pesticides.

Under-sink carbon block or activated carbon filters commonly come with NSF 401 certifications. Inline refrigerator filters and countertop filters may also be certified to NSF/ ANSI standard 401.

NSF P231

NSF P231 applies to drinking water purifiers that offer microbiological contaminant reduction. Water treatment filters with an NSF P21 certification offer a performance that meets NSF’s standards for purifying water at the biological level and making it safe to drink.

If you’re looking for a water filter that offers the highest-purity water, you won’t go wrong opting for a filter with an NSF P231 certification. Filters are certified to reduce or remove a number of microbiological contaminants if they have achieved this NSF standard, including bacteria, viruses, and cysts.

When applying for an NSF P231 certification, companies will need to allow their product to undergo rigorous testing by the NSF, in order to prove it capable of converting a challenging microbiological compromised water source into clean, purified drinking water.

Typically, countertop filters and under-sink filters can apply to be certified to reduce microbiological contaminants.

NSF P477

NSF P477 focuses on microcystin reduction. Microcystins are a class of cyanotoxins, a group of bacterial contaminants, that have been found in drinking water sources in the US. Otherwise known as blue-green algae, these contaminants can be highly toxic and harmful to human health.

A water filter that has an NSF P477 certification is certified to reduce cyanotoxins from drinking water.

In 2015, the Environmental Protection Agency set a new health advisory that dictated cyanotoxins should be present below 0.3 ยตg/L in drinking water for children aged six and under, and below 1.6 ยตg/L for adults and older children.

A number of point-of-use water treatment systems now offer at-home microcystin contamination reduction, and currently, only POU systems can apply for an NSF third-party certification for this purpose. This is due to the limited availability of the microcystin chemical that’s needed for testing.

It’s common for NSF P477 certified filters to also be certified to NSF standard 53.

NSF P473

PFOS (perfluorooctanesulfonic acid) PFOA (perfluorooctanoic acid) in drinking water pose significant health concerns, and NSF P473 was developed in response to this particular group of man-made drinking water contaminants.

While PFOS and PFOA have been phased out of production, these chemicals are known as “forever chemicals”, which means they linger in the environment for a long time.

In order to be certified for NSF standard P473, a water filter should offer performance data that proves it is capable of PFOS/PFOA contaminant reduction. The NSF will also carry out its own extensive testing on a system to determine that it can reduce these chemicals to below the EPA healthy advisory limit (70 PPT, or parts per trillion).

When water systems have an NSF P473 certification, you can be sure that their PFOA/PFOS contaminant reduction claims are true. The system also won’t leak or add anything dangerous to your water during filtration, and its performance data, product label or advertising won’t be misleading.

Countertop and under-sink water systems are most likely to have an NSF P473 certification.


Finally, NSF/JWPA P72 applies to drinking water systems that offer iodine radioisotope reduction.

This certification was introduced in 2012 by the NSF in collaboration with the Japan Water Purification Association (JWPA), following a tragic earthquake in Japan in 2011. Manufacturers of filters offering contaminant reduction claims for iodine, including radioactive iodine, can apply for an NSF/JWPA P72 certification.

Carbon block/ activated carbon, ion exchange and reverse osmosis systems can all be tested and certified to this standard. NSF testing found that absorptive activated carbon media is capable of effectively reducing iodine; as are reverse osmosis membranes and point-of-use ion exchange technologies.

Water systems are unable to apply for an NSF/JWPA P72 certification alone. In the US, a system will also have to meet NSF standard 42 for reducing asthetic effects, or standard 53 for health effects if adsorptive media is used. For RO water systems, a the unit should have an NSF standard 58 certification.

๐Ÿ… How Manufacturers Achieve NSF Standards Certification

To be certified by the NSF, a company will be required to complete a number of application steps.

  • The company submits an application, providing information about their product. A parts list, user information, and drawings may be submitted at this stage.
  • This application will then be reviewed by NSF’s technical team. Test samples will also be requested during the reviewal process.
  • NSF representatives will visit the company’s production facility to perform an audit and confirm information about the product.
  • NSF privately tests the product in their own laboratory. This will determine whether the product lives up to the company’s claims.
  • Finally, the NSF will carry out one last technical evaluation before determining whether a certification can be granted.

Achieving an NSF certification is no easy feat. It’s an expensive process, and some companies have chosen not to obtain NSF certifications because of the costs involved.

However, there’s no denying that being certified to NSF/ ANSI standards offers peace of mind to customers who have never bought from a certain manufacturer before.

Achieving an NSF certification isn’t only about removing specific contaminants. For the majority of NSF certifications on this list, the manufacturer should also provide evidence that:

  • The system adds nothing dangerous into the water
  • The system is structurally sound
  • No product labeling, advertising or literature is misleading
  • Production processes and materials remain consistent in design and quality
  • The manufacturer’s claims of contaminant reduction, as disclosed in the product’s performance data sheet, are accurate

๐Ÿ“Š Evaluating Competitive Products Using NSF Standards

NSF standards make it much easier to compare drinking water treatment options. But before you get started, it’s wise to consider your filtration objectives.

If you don’t know what contaminants you’re dealing with in your water source, you’ll struggle to figure out which filter is best for you. It’s also wise to be aware of additional important filter factors, including flow rate and filter capacity.

It’s easy to assume that a product offers exceptional performance if it has an NSF certification. However, while an NSF certification does offer some security when it comes to contaminant reduction claims, systems can vary when it comes to durability, filter lifespan and structural integrity.

When you notice a system has an NSF certification, do your research. Find out which specific contaminants the filter is certified to remove.

Marketing materials can sometimes be a little misleading. For instance, a filter might only be certified to remove chlorine, but if you read that it’s “NSF certified to standard 42”, and you don’t know much about this certification, you might think it is certified to remove all the contaminants listed.

You should also be aware of claims such as “tested to NSF standards” or “meets NSF standards”. At first glance, it may seem that the water filter is NSF certified. However, it most likely means that the system has simply been tested in-house by the manufacturer or a third-party they hired to do so. Be careful not to be misled by these statements.

As mentioned earlier in this guide, the easiest way to determine whether a product is truly NSF certified is to visit the NSF’s certification catalog. Here you can browse through products or search for a specific drinking water treatment unit to check for an independent third-party certification.

โ” Frequently Asked Questions

Should I still buy a water filter if it doesn’t have an NSF certification?

It’s your decision. There are plenty of water fitlers out there that don’t have an NSF/ANSI certification. The Big Berkey is perhaps the most obvious example. There are a number of reasons why a company may decide not to get its products tested and certified, and generally, a lack of certification isn’t because a system doesn’t live up to its performance claims.

However, you are taking a gamble if you decide to purchase a system that isn’t certiffied. You have no way of knowing whether the system is capable of meeting its reduction claims.

My advice is to look at product reviews to see how a system performs for customers like you. You could also arrange for laboratory testing of your water before and after using the filter to check that it greatly reduces or removes the expected contaminants.

How do I know whether a filter is certified by the NSF?

If a manufacturer claims that a product is certified by the NSF, they should have official documents from NSF testing to prove this.

Don’t just take a manufacturer’s word for it. It’s easy for anyone to say that their product is NSF certified, but without the documents, you have no reason to believe them.

If you can’t find any official information visit the NSF’s catalog and search for the product on there. NSF lists all of its certified products online. If a so-called certified water filter isn’t in this list, that’s a big red flag.

You can always contact the company for extra clarity if you’re unsure.

  • Brian Campbell
    President & CEO, CWS, CWR

    Brian Campbell, a WQA Certified Water Specialist (CWS) and Certified Water Treatment Representative (CWR) with 5+ years of experience, helps homeowners navigate the world of water treatment. After honing his skills at Hach Company, he founded his business to empower homeowners with the knowledge and tools to achieve safe, healthy water. Brian's tested countless devices, from simple pitchers to complex systems, helping his readers find the perfect fit for their unique needs.

8 thoughts on “NSF 42, 53, 58, 401 & More: Water Filter Certifications Explained”

  1. Avatar for Brian Campbell

    Hello and thank you for this wealth of information. I am about to move into a new home and it will have a well. I am concerned about n-fowleri, brain eating amoeba. Can you suggest a whole house filter for peace of mind. Thank you!

    1. Avatar for Brian Campbell

      Many, but what works for one situation might not be sufficient for another. This is why testing before investing in a system is vitally important.

  2. Avatar for Brian Campbell


    Thank you for this information.
    I’m principally interested in finding a product that I can add to my whole house filtering system. I have read about the NSF P473 standard for under the counter applications, but I don’t see a similar stand for whole house applications. I understand that GAC filters using bituminous coal would filter PFOA and PFOS, et. al. I have a well. Would have any thoughts about my application?

    Best regards,

    Quentin Reader

    1. Avatar for Brian Campbell

      Hey Quentin great question! You can also look for products that are certified for the reduction of PFOA/PFOS under NSF/ANSI 53. Are you looking for a tank or cartridge based system? What existing treatment do you have in place?

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