Why (And How Much) You Should Know About Water Filter Certifications

When our team of reviewers is looking at a new water filter system, what do you think we check for first? It’s not the price, or the build quality, or even the ease of installation. It’s the filter’s certifications.

Two governing bodies are in charge of providing certifications for water filters, and they’re what separates marketing claims from real performance. If you want a water filter that’s guaranteed to make your water cleaner and better tasting, start by looking at its certifications.

In this guide, we’ll give you the complete rundown of who’s providing this valuable information. That includes a little bit about the National Sanitation Foundation (NSF) and the American National Standards Institute (ANSI). Then we’ll cover the certifications you should be looking for in your water filters, from the most common to the most obscure.

Who Determines Drinking Water Standards?

Worker Inspecting Water Pump And Pipes

Under the U.S. Safe Drinking Water Act (SDWA), the Environmental Protection Agency (EPA) sets legal limits on over 90 contaminants in drinking water. The EPA provides national guidelines, while the SDWA allows individual states to set even more stringent requirements if they so desire. Together, this sets the standard for all of the municipal drinking water that flows through homes in the United States.

Why does this matter? Because the EPA’s standards set safe levels for contaminants — but that doesn’t mean that water is going to taste good. And in the case of what are called emerging contaminants — a class of problematic molecules that come from sources like chemical runoff and pharmaceuticals — the EPA hasn’t actually set standards yet for their levels.

That’s where water filter certification groups step in. They take an even harder line stance on what contaminants each filter can remove. Let’s take a closer look at what makes each organization tick.

The Certification Groups: NSF and ANSI

Two organizations are all important in deciding water filter certifications: The National Sanitation Foundation (NSF) and the American National Standards Institute (ANSI).

The NSF has been dedicated to promoting better health since its inception in 1944. They’re an independent global organization whose duties include:

  • Testing, inspection, and certification
  • Standards development
  • Training and consulting

And they’re involved in the following industries:

  • Automotive and aerospace
  • Building and construction
  • Food
  • Water
  • Health

This means that overall, the NSF provides important health and safety guidelines for our most essential products and services.

ANSI is a private, non-profit organization founded in 1918. They partner with the NSF to further create and enforce specific product design guidelines. Their broad reach and huge support from multinational companies make it easier to coordinate different aspects of certification.

Together, the NSF and ANSI provide a comprehensive solution to verifying product quality claims. In the case of water filters, this means certifying a filter’s build quality and its ability to effectively filter out specific contaminants.

The Certifications

certificate example

Each of the certifications awarded by the NSF and ANSI is number-coded. This makes it easy to know at a glance what any given water filter can handle — and whether you need to look elsewhere for your water filter needs. With that in mind, let’s examine each of the relevant certifications in greater detail.

NSF 42 Certification

Certification 42 is the most common one that you’ll find in every class of water filter. It’s a guarantee that a given filter will remove aesthetic impurities. That means bad tastes, smells, and cloudy water can all be fixed by a filter with this certification. This is our baseline comparison; if a filter doesn’t have certification 42, it’s unlikely to be particularly useful.

NSF 44 Certification

Certification 44 deals with a special category of filters that use cation exchange resins. It establishes the guidelines for how much a filter can reduce water hardness. And it also certifies a certain level of build quality and structural integrity of the system. An uncommon certification, it’s what you’ll want to look for if you’re looking to soften your water.

NSF 53 Certification

Certification 53 is one of the “big three” certifications, alongside 42 and 401. According to the NSF, it “establishes minimum requirements for systems designed to reduce specific health-related contaminants”. That means any filter with certification 53 is guaranteed to reduce harmful molecules like lead, volatile organic compounds (VOCs), bacteria, and viruses. If you’re concerned with your water quality’s effect on your health, this certification will fix it.

NSF 55 Certification

Certification 55 is specific to filters that use a UV light system. In these filters, UV light is used to kill or deactivate bacteria, viruses, and cysts. It’s not seen often in filter systems, though some reverse osmosis filters use it as a final cleansing stage. 

NSF 58 Certification

Certification 58 is specific to reverse osmosis filter systems. It guarantees the effectiveness of the system’s reverse osmosis membrane. That means it’s certified to remove or reduce the whole range of contaminants indicated by the EPA, and that the structural integrity of the filter is up to par.

NSF 62 Certification

Certification 62 is specific to distillation systems. It guarantees the build quality and filtering capabilities of these systems, which heat water to a boiling point and collect the purified water vapor. Some contaminants like VOCs, though, can easily convert to gas and be carried over in the distillation. That’s why you’ll often see distillation systems paired with certifications 42 and 53, to ensure that contaminants are fully removed.

NSF 177 Certification

Certification 177 is used only for showerhead filters. It means that the filter is certified to reduce freely available chlorine. But it makes no other claims for reducing other contaminants.

NSF 244 Certification

Certification 244 is one of the most uncommon of all. Filters with this certification are able to protect against intermittent bacteria and virus contamination. For example, they’re useful for keeping your water safe during a boil water advisory. Manufacturers of these types of filters can claim bacteria, viruses, and cysts reduction for their products.

NSF 401 Certification

Certification 401 is perhaps the most sought-after certification in current filter systems. It guarantees protection from emerging contaminants. As of now, 15 different emerging contaminants have been identified, ranging from pharmaceutical residue to pesticides to microplastics. Filters with this certification are guaranteed to remove or reduce one or more of these contaminants, protecting against dangers that are not yet regulated by the EPA.

NSF P231 Certification

Certification P231 filters are verified as microbiological purifiers in accordance with guidelines from the EPA. They’re often recommended for well water, since they remove or reduce pathogenic viruses, bacteria, and cysts. In short, this means that P231 filters can make even the most biologically contaminated water safe to drink.

NSF P473 Certification

Certification P473 was created in direct response to the presence of PFOA/PFOS in drinking water. These are man-made chemicals that were in wide use until the early 2000s, which have since been phased out across the globe. P473 filters are guaranteed to remove the presence of these man-made chemicals in your water.

NSF P477 Certification

Certification P477 is about as specific as NSF/ANSI standards get. It means that a filter is certified to remove microcystins, a group of toxins produced by blue-green algae.

How Manufacturers Get Certified (and Why That Matters)

Scientist Testing Water Quality

I’ll put this bluntly: Without the NSF and ANSI to certify water filters, finding an effective filter would be nearly impossible. 

Companies could make whatever claims they wanted without needing to provide information to back it up. By paying close attention to what certifications a filter system has received, you can rest assured that it’s actually cleaning and purifying your water in the way you desire.

The certification process for water filters is a rigorous one, with seven steps.

Step 1 is an application to be admitted to the NSF’s testing process

Step 2 is where the company submits detailed information on product formulation, toxicology, and product use information.

Step 3 is where the NSF’s technical team performs a thorough review of the formulation and parts list for the filter system in question.

Step 4 is an on-site audit, where NSF technicians tour the production facility and gather samples of products and materials used in the filter system.

Step 5 has these technicians return to the NSF laboratory, where the filter and its components undergo a battery of tests to prove their efficacy.

Step 6 is a final technical evaluation that takes into account every step before it. It’s a final check-over that acts as a safeguard against anything that might have been missed in the process.

Step 7 is the awarding of certification, and companies must renew this certification annually by going through steps 2 through 6 again.

Taken together, this seven-step process guarantees that any products that carry an NSF/ANSI certification are fully tested and guaranteed to perform their advertised functions.

Using Certifications to Compare Similar Products 

Having all of these certifications at your fingertips will let you make savvy comparisons between different water filters. 

For example: If you found two under sink filters at nearly the same price, which one should you choose? In most cases, it’s best to choose the one with the most robust series of certifications. If one filter system is only rated to Certification 42, and another is rated to Certifications 42, 53, and 401, the second system is obviously a more effective filter.

In situations where two or more filters have the same certifications, though, it’s best to look towards price, build quality, and ease of installation to make your choices.

FAQs for NSF/ANSI Water Filter Certifications

To wrap things up, let’s take a quick look at some of the questions we’ve heard asked most often about water filter certifications.

Is there an NSF water filter certification lookup?

The NSF helpfully provides a database of all the companies that manufacture water filters, and which certifications their products have received.

How do I find out if something is NSF certified?

Manufacturers will proudly display their NSF certifications on their products’ packaging, as well as on their websites. If that fails, use the search function provided above to verify that a company has received certifications for their water filters.