NSF 42, 53, 58 and 401 – Is it necessary to buy a certified water filter?

Any product which is designed as an aid to people’s health and safety should have to pass rigorous testing. Though not a legal requirement for water filters, it is a huge plus point if the manufacturer can offer certification to prove the quality and effectiveness of their filter.

This certification is not just based around the appearance or materials of the water filter. It is based around which items and elements are filtered out. Each of the NSF certification numbers means a different level of filtration, and that it has been independently tried and tested.

What is the NSF and why does their certification matter?

According to their website, “NSF independently tests, audits, certifies, trains and consults for the food, water, health science, sustainability and consumer product sectors.”


The NSF brand is built around decades of these independent tests. This means that consumers and retailers have come to trust the NSF logo. Their certifications are wide-reaching and used in a variety of different industries.

What Each NSF Certification Means

So, what do the certifications mean for your filter? Why are there numerous types of filter and which will best suit your own needs? To answer this question, we need to look at each of the certifications, NSF 42, 53, 58 and 401.

NSF 42

NSF 42 is a certification based around the taste and smell of water. NSF 42 filters have the ability to remove chlorine as well as other unpleasant impurities which can cause your water to have a strong and unpleasant odor.

NSF 53

A filter can only be awarded NSF 53 certification if it treats (and effectively reduces) at least one of the contaminants with health effects, as detailed by the EPA (Environmental Protection Agency). This may mean lead and other heavy metals or volatile organic compound. NSF 53 certification is often used on carbon filters and other methods of filtration, as opposed to RO filters.

NSF 58

NSF 58 is the certification specifically designed for reverse osmosis filters. Similar criteria as the NSF 53 apply. These filters must reduce contaminants as outlined by both the EPA and Health Canada.

NSF 401

The 401 certification is based around ‘emerging contaminants’. In the time after a harmful contaminant is created and enters our water systems, it can take a while for them to be formally recognized and regulated under FDA standards. This means that other certifications based around the FDA do not apply. The NSF 401 certification means that the filter reduces at least one one ‘emerging contaminant’. There are currently 15 of these types of contaminants, as shown here. They usually remain in the emerging category until their exact health threat has been established.

FAQs About NSF Certification

How is the ability of the filter proved?

In order for a filter manufacturer to get this certification, they must provide a data sheet providing huge amounts of information on their product, and the NSF may then run their own tests on a product to check that it is reducing the contaminants it claims to. Only then can it issue the certificate.

Can a filter have multiple NSF certificates?


 Yes. The filter can have more than one of the certifications listed above. If they fit the criteria for multiple NSF ratings then they can be advertised with multiple certifications.

Is it Necessary to Buy a Certified Water Filter?

Although there are effective products out there which do not have this certification, the NSF certificates are designed to provide safety in your purchase and give you peace of mind that your water filter can do what it claims to be able to. The certification is a guarantee that the filter has been tested and data has been provided on how effective it is at removing various contaminants.

It is worth taking into account that the NSF certification is not the ultimate best way of judging a filter. Because of the way the filters are certified, they only need to be able to treat one contaminant to carry the certification. This means that filters which treat one contaminant can have the same rating as one that treats eight or nine. This is why it is best to read water filter reviews and only take NSF certification into account for part of your buying decision.

It is definitely advisable to look out for certification from the NSF when you are buying a water filter. The National Sanitation Foundation exists for a reason; to suggest safe products. A full list of their approved products can even be searched via the NSF website.