Water filter certifications explained: Interpreting NSF, ANSI, & lab reports

nsf seal of approval

The seal of approval (What you’re looking for). Source: NSF

Key points

  • In a rush? For those looking to filter tap water that’s generally safe to consume, choose a product with NSF certification number 42.
  • If you need a filter capable of turning potentially unsafe sources into drinkable water, only consider products with NSF numbers 53 and/or 244.

Let’s face it, the home water filter market is flooded with different brands and types of filters to choose from.

Perhaps you have a clear idea of the contaminants you’re looking to remove from your water supply and the type of filter required to do that job. But more likely, you’re simply on a quest for purer, better-tasting water—with the added peace of mind that you’re not consuming anything really nasty.

Whether you’re a filtering aficionado or a casual contaminant-remover, a key part of your purchasing process should be determining which certifications your filter needs to have. To help, here are the most common contaminants in tap water, and the NSF relevant stamps of approval a filter needs to have, in order to be able to claim it can remove them.

Certification boards

There are several authoritative certification boards for water filters, the most universal being the NSF:

  • NSF International. Founded in 1944 as the National Sanitation Foundation, NSF International provides safety assurance for a wide range of products and product uses, from aerospace to medical technology. When it comes to home filtering, NSF claims to have the world’s largest test facility, with thirty testing rigs.
  • ISO. The International Organization for Standardization is “an independent, non-governmental international organization with a membership of 164 national standards bodies.” Based in Switzerland, the body provides baselines and standards for the industry and home processes, such as food safety and child seats for cars.
  • WQA. The simply named Water Quality association tests home filter products, as well as acting as a database for filter certifications. Their Gold Seal Product Certification Program ensures that filters meet their own—or NSF/ANSI equivalent—standards.
  • ANSI. For the North American market, the American National Standards Institute has official parity with the ISO and NSF for water filter certifications. The same goes for CAN 60 regulations in Canada. This means that, if you see an ANSI or CAN badge, you’re good to go!

(Because NSF international standards are the most widely used and equivocated certifications, we’ll stick to those for this article.)

Chlorine, ozone, and other treatment traces

Treatment plants purify and remove water long before it reaches your home. To do this, common chemicals and gases are often used to ensure that parasites and disease-causing organisms won’t reach your glass.

While useful, chemicals such as chlorine can have a pungent taste and smell, even in small amounts. For this reason, a large number of products on the filter market are designed specifically with aesthetic or non-health-related contaminants in mind. Most commonly making use of activated carbon filters, these systems are great for removing bad-tasting but safe particulates and soluble matter that’s often present in both public and private drinking water.

NSF/ANSI certification

  • Standard 42. This standard covers the safety of filter materials, product structural integrity, and claims related to aesthetic, non-health-related contaminant reduction performance.

Lead, copper, and heavy metals

Thanks to old pipes and faucet fittings, as well as recent high-profile contamination cases, many are seeking out filters to be sure that there drinking water is free from heavy metals—many of which have no taste, smell, or visual identifier.

NSF/ANSI certification

  • Standard 53. With this standard, you can feel confident that your filter is removing lead and other volatile organic chemicals (VOCs). While they’re at it, these products are also capable of reducing or removing health-related bacterial contaminants such as Cryptosporidium and Giardia (see below).

Algae, bacteria, and organisms

Home filters and bacteria contamination is somewhat of a grey area. There are consumer products totally capable or ridding your drinking supply from microorganisms such as Giardia, which can cause cramps, diarrhea, and fatigue, or blue-green algae, which may cause mild respiratory effects and hayfever-like symptoms.

However, filtration devices are intended to be used on pre-treated water, which is already certified safe.

Well water, on the other hand, is not pre-treated and may contain these bacterias. A more powerful, NSF-certified well water filtration system is recommended if your well has tested positive for these bacterias.

E. coli or coliform bacteria isolated and culture

NSF/ANSI certification

  • Standard 53. As above, this standard is the minimum requirement for filters claiming to reduce health-related contaminants, such as Cryptosporidium and Giardia.
  • Standard 58. This is the NSF reverse osmosis filter standard. When an RO filter meets this certification, it can sufficiently reduce the presence of cysts, bacteria, and nitrates.


Your average home filter device is unlikely to be able to filter at a fine-enough level to remove viruses from water. However, the use of multi-stage reverse osmosis and ultraviolet systems are capable of filtering to this high standard.

NSF/ANSI certification

  • Standard 58. Reverse osmosis standard.
  • Standard 244. This standard sets the minimum requirement for reducing microorganisms, bacteria, viruses, and cysts in microbiologically safe drinking water.
  • Standard 55. NSF standard for UV water treatment, able to disinfect or remove microorganisms including bacteria and viruses—or able to reduce normally occurring nuisance microorganisms.

Chemicals and nonorganic compounds

Lastly, there’s a category of possible tap water contaminants that don’t count as treatment plant chemicals, nor are they are living microorganisms. These are the trace chemicals produced as a result of our modern, industrialized lifestyles, which can find their way into drinking water and stay-put—even after public filtering.

NSF/ANSI certification

  • Standard 244. This standard sets the minimum requirement for reducing microorganisms, bacteria, viruses, and cysts in microbiologically safe drinking water.
  • Standard 401. This standard is a newer NSF introduction, designed to address up to 15 individual contaminants, which have been identified in published studies as occurring in drinking water. These are:
    • Prescription medication traces such as anti-anxiety, birth-control, and beta-blockers drugs.
    • Ibuprofen and Naproxen.
    • Herbicides and Pesticides
    • DEET insect repellent.
    • BPA (a chemical compound found in some plastics and considered not safe for consumption by most bodies.)