Do Water Filters Remove Microplastics?

Certain filters can reduce microplastics, but it depends on what the filter is made of. The biggest thing to look for is the test behind the label. Carbon block filters are particularly well suited to blocking microplastics. In one independent certification test, the average reduction was 98.9%.

The filter behind that 98.9% certification result is the BOROUX Foundation Filter. BOROUX proudly publishes the report (see the test report), so you can check the numbers yourself.

If you're trying to work out what's in the water your family drinks, here's the useful part: a badge on a box isn't proof, but the test behind it is. The sections below explain, in plain terms, what a good test measures and how you can check a claim yourself.

What are microplastics?

Microplastics are tiny particles of plastic, generally defined as being less than five millimeters in size, which is about the size of a sesame seed or smaller. These particles are either intentionally produced at a small size, such as in microbeads found in personal care products, or they form as larger plastic debris breaks down over time.

The EPA stretches the category from 5 millimeters all the way down to 1 nanometer, which is a billionth of a meter, and calls anything under 1 micrometer a nanoplastic. The size range behind drinking-water filter claims is narrower: 1 to 5,000 micrometers. A micrometer is a millionth of a meter, and you'll see why that unit matters in a moment.

For a filter, the headline definition isn't the number that counts. What counts is the size range of particles the filter was actually tested on, for example particles between 0.5 and 1 micrometer across. A filter can be certified for one size range without saying anything about smaller particles, which is worth remembering whenever a label just says "microplastics."

Next question: how much of this is in your glass, and would switching to bottled water help?

How much microplastic is in tap water, and is bottled water better?

Start with a tap, if you've read that microplastics turn up in drinking water, you're not imagining it, and it isn't a sign that your water is unusual. A widely cited study by Kosuth and colleagues tested 159 tap water samples from 14 countries and found human-made particles in 81% of them. The US average, from 2017 sampling, was 9.24 particles per liter, the highest national average in that dataset. Most of what turned up was fibers between 0.1 and 5 millimeters long. The study ran samples through a 2.5 micrometer filter and counted particles from about 0.1 millimeter up, so it can't tell us what's happening at the much smaller sizes that filter tests measure.

It's natural to wonder whether a case of bottled water is the workaround. The research suggests it probably isn't. A 2024 PNAS study estimated about 240,000 plastic particles per liter in three bottled water brands, roughly 90% of them nanoplastics. A 2026 study by Hart and Lenhart compared six bottled brands with four treated municipal supplies in one region and found significantly higher micro- and nanoplastic concentrations in the bottled water, especially for the smaller particles.

If you're buying bottled water to get away from microplastics, these studies give you reason to doubt that it helps. There's more on that in why plastic bottled water isn't the safer default.

So if bottled isn't the answer, what about a filter in your own kitchen?

Do water filters remove microplastics? It depends on how they filter.

It comes down to one question: does the filter physically strain particles out of the water? Microplastics are solid particles, so what matters is how big they are compared with the gaps the water flows through. That's where a unit called the micron comes in.

Microns, also known as micrometers and represented as µm, are a unit of measurement equating to one millionth of a meter. To put it into perspective, 1,000 microns is equal to just one millimeter. This is roughly the thickness of a plastic credit card or the wire of a standard paperclip. A filter's micron rating tells you the particle size it is designed to strain out.

Dissolved chemicals, such as lead and PFAS, are a different story. They don't get strained; they stick to carbon through a process called adsorption. A filter that does well on chlorine won't necessarily catch plastic particles, and a filter that catches particles won't necessarily handle every dissolved contaminant.

A 2023 study of pour-through pitchers shows why this matters. Carbon plus ion exchange on their own did poorly on particles. Adding a membrane stage brought reductions of 46-86%. Carbon is good at chemistry, but "carbon" alone isn't a microplastics claim. The word on the box matters less than whether anyone tested for particles.

The table below sorts the common filter types. It refers to NSF/ANSI 401, the standard behind microplastics claims.

Carbon block filters show up in that table as "some products." So what is a carbon block actually doing to a plastic particle?

How does a carbon block filter reduce microplastics?

For particles, the job is mechanical. The tiny pores of the carbon block are so small that they physically block and trap tiny particles, functioning like a sieve or strainer. Anything bigger than the gaps gets caught, which is how a filter can reduce plastic particles in a tested size range.

Dissolved chemicals are a separate job for activated carbon. Chlorine and volatile organic compounds (VOCs) stick to the carbon's surface through weak intermolecular forces called van der Waals forces. That's adsorption, with a "d." It isn't magnetism, and it isn't how particles get caught.

What does a microplastics test look like? NSF/ANSI/CAN 401

NSF/ANSI/CAN 401 is the standard for emerging contaminants, meaning things like microplastics, pharmaceuticals and pesticides whose effects aren't yet fully researched. Its microplastics claim uses the same mechanical test as NSF/ANSI 42 Nominal Particulate Class I, the particle-reduction claim.

According to NSF staff, the test works like this: a lab pours water containing ISO fine test dust through the filter. The water has to carry at least 10,000 particles per milliliter, and the filter has to reduce at least 85% of the particles between 0.5 and 1 micrometer. That narrow size range is a conservative stand-in for the full 1 to 5,000 micrometer microplastics definition, on the logic that a filter that catches the smallest pieces in the test should catch larger ones. Anything smaller than that range sits outside the test.

BOROUX Foundation Filters are a worked example, because BOROUX publishes the certification test numbers. In the report from IAPMO R&T Lab (NJ), an ISO/IEC 17025 recognized laboratory (the international standard for lab competence), dated October 28, 2025, the average challenge was 6,500,000 particles per milliliter and the average reduction was 98.9%, against the 85% requirement. The WQA Gold Seal certificates are dated June 2025. IAPMO is a plumbing and mechanical standards organization, and WQA, the Water Quality Association, is one of the bodies that certifies filters.

BOROUX Foundation Filters are WQA certified to NSF Standards: NSF/ANSI 42, NSF/ANSI/CAN 372 and NSF/ANSI/CAN 401. Those three mean different things:

• NSF/ANSI/CAN 401 is the microplastics performance claim.
• NSF/ANSI 42 includes Nominal Particulate Class I, which uses the same 0.5-<1 µm particle test.
• NSF/ANSI/CAN 372 trips a lot of people up. It's about the filter's own materials: it confirms the parts don't add lead to your water. It says nothing about whether the filter takes lead out of water. Those are two different promises.

You can check this yourself. The WQA listing names the 3-Gallon Water Filter System (BX-L-SYS-3) and the 1.8-Gallon Water Filter System (BX-L-SYS-COM) with the BX-FND9-2 Foundation element. The listing shows the claim. The 98.9% is BOROUX's published certification test result, not something the listing states. The listing also notes that claims of capacity or rated service cycle are not applicable for mechanical filtration, so "lasts X gallons" is a different promise from "strains particles in this size range."

The certifications page lists every standard BOROUX holds: 42 and 401 are the performance certifications, and 372 is materials only.

The other question on most people's minds is whether any of this matters for your health.

Is it harmful? What the research says so far.

Research is active, and a health risk from tap water has not been established.

The WHO's 2019 review concluded that microplastics in drinking water don't appear to pose a health risk at current levels, while calling for more research. The EPA is studying health effects. There is no federal drinking-water limit for microplastics, and California is the first state to require monitoring; its treated-water phase is due to begin in fall 2026, with no results yet.

More recent human-tissue studies have sharpened interest without proving cause. A 2024 NEJM study of patients having carotid surgery found an association between micro- and nanoplastics in plaque and a higher risk of heart attack, stroke or death. The authors were explicit that this was an association, not causation. A 2025 Nature Medicine study found higher brain concentrations in more recent samples and in descendants with a dementia diagnosis, again without a causal claim. And a 2025 state-of-the-science review found no direct evidence of human exposure to micro- and nanoplastics in water, and growing laboratory and animal evidence of harm. It also said the lack of standard methods limits comparisons.

Wanting fewer plastic particles in your family's water is reasonable. The research so far doesn't show that tap water at current levels harms you, and it doesn't settle the question either. There's no need to panic, and no need to ignore it. A filter with a real, checkable test is a sensible middle path.

So if you'd like to do something about it, how do you tell a real claim from a vague one?

How can you check a microplastics claim, or your own water?

First, the honest limit. The water quality report from your utility doesn't list microplastics, and there's no standard consumer microplastics test right now, so a generic home test kit isn't a microplastics panel. Don't spend money expecting it to be one.

What you can verify is the certification. Open the WQA, IAPMO or NSF listing and match the product and model number, not just the brand. BOROUX's 401 listing names specific system configurations and the replacement element, which is exactly the detail a vague badge can blur. You can also test your water for regulated contaminants at a lab; that is where water testing is most useful.

Can a filter put plastic back into my water?

It can happen with some pitchers. In the 2023 study, carbon plus ion exchange on its own ended up with more particles of PET (polyethylene terephthalate, the clear plastic used in most water and soda bottles) in the filtered water than went in. If that worries you, and especially if your kids drink from it, look at the housing as well as the filter. BOROUX's systems are stainless steel, so very little plastic touches your water.

Which systems carry the claim?

If a publicly checkable microplastics claim is what you're after, the BOROUX Foundation Filters carry it. The WQA 401 listing names them together with the BOROUX 3-Gallon Water Filter System and 1.8-Gallon Water Filter System.