Reading Microplastic Filter Tests: Particle Size, Challenge Counts and Conditions

A microplastics reduction percentage describes only the particles that were in the test water: the size band they fell in, how many were added per milliliter, and which cartridge they passed through. Two published results, such as an average of 96.48% on one sheet and an overall 99.8% on another, can come from different particle counts and carry different result labels, and the data sheet row behind each one shows which.

Under-sink reverse osmosis is one way to bring microplastics filtration to the kitchen tap, and the Viomi M1 suits that job, removing 99%+ of microplastics in independent testing by SGS. Published data sheets from AquaTru, PUR, Brita and Clearly Filtered each print their microplastics result in a slightly different way, and reading them side by side shows which fields sit beside a percentage on a data sheet row.

Where the Particle Size Sits on a Data Sheet

The FDA describes microplastics as pieces of plastic "typically considered less than five millimeters" in at least one dimension, and nanoplastics as "typically considered to be less than one µm, or micron, in size" (FDA). Five millimeters is 5,000 microns, so the word on a filter box covers a huge span of sizes. A test result narrows that span to one band, and on several data sheets the band is printed inside the row label itself.

On the Brita Elite performance data sheet, the row reads "Microplastics, particles 0.5-1 µm" under NSF/ANSI 401 (Brita Elite PDS). A close neighbor of that band, "Particles 0.5 to < 1 µm", appears in the 401 table on AquaTru's Classic sheet (AquaTru Classic PDS), with a less-than sign on the upper end. In both cases the band is part of the claim, and the exact wording of its edges travels with the result it describes.

The standard heading above a row deserves a second look, and the PUR pitcher sheet shows why (PUR pitcher PDS). Its 401 table carries a row labeled simply "Microplastics", and the size band appears elsewhere, in a particulate row under NSF/ANSI 42 that reads "Nominal Particulate (Class I, particles 0.5 to <1μm)". The Brita sheet also prints a "Particulate Reduction (Class I)" row under 42 alongside its microplastics row under 401. Particulate and microplastics rows are separate claims under separate standards, and the same PUR table shows them recorded separately: its PPF900Z cartridge has a result for larger Class VI particulates (50 to 80 µm) while its microplastics row reads "Not Certified". When a product page mentions "particulates" and "microplastics" together, the standard printed above each row shows which claim each word belongs to. Which filter formats carry a microplastics listing at all is laid out in the guide to water filter brands designed for microplastics.

A Reading Table for One Microplastics Row

A microplastics row is easiest to read one column at a time, starting from the row label and moving across to the result and the cartridge it names.

Sources: AquaTru Classic PDS, PUR pitcher PDS, Brita Elite PDS, Clearly Filtered pitcher performance data.

One pitcher sheet can cover more than one cartridge. PUR prints two replacement filters in one table, and the microplastics row gives 99.8% for the PPF951K while marking the PPF900Z "Not Certified". The sheet lists both replacement filters for the same set of pitcher models, so the part number on the cartridge box is what connects a household to the result. AquaTru's sheet works the same way at the system level: it names six AT2000-series models, and its replacement list gives the RO membrane its own part number, AT2002, with a replacement interval of "every 24 months or 1200 gallons, whichever comes first."

Pass Marks and the Kind of Result Printed

The 85% figure that appears on several microplastics rows is the requirement, and the result sits in its own column. Across the three sheets that print both, the filter's figure lands at 96.48% under an "Average Reduction" heading on the AquaTru Classic sheet, at 99.8% in an "Overall % Reduction" column for the PUR pitcher cartridge, and at 99.6% beside Brita's "85%*". Reading across the two columns shows that each filter cleared the line and by how much on the test it was given.

The column heading above a result names what kind of figure it is. AquaTru labels its column "Average Reduction" and PUR labels its column "Overall % Reduction", and Clearly Filtered states its basis directly on its pitcher page: "The filter results presented are the maximum removal percentage." That pitcher, according to the same page, is certified by NSF to NSF/ANSI 42 and 372, and its microplastics figure comes from additional testing at an ISO 17025 laboratory now operating as IAPMO New Jersey. A maximum, an average and an overall result are reported on different bases, so the label printed with each percentage belongs in any comparison of two results.

Each sheet also prints its own caution about lab conditions. PUR writes that "testing was performed under standard laboratory conditions, actual performance may vary," and AquaTru uses nearly the same sentence. That line explains what a reduction figure is: a measured result from a controlled test water, reported for the cartridge named on the sheet.

How Many Particles Went Into the Test Water

The challenge count is the amount of test material in the water before it reaches the filter, and it is printed per unit of volume. The PUR and Brita sheets give "at least 10,000 particles/mL" and ">10,000 particles/mL", and AquaTru's Classic sheet lists 1,400,000 particles/mL. Those three use the same unit, so they can be read side by side. A count does not rank one filter above another on its own, since each sheet pairs its count with its own requirement and result, but it does show how heavily loaded the test water was when the percentage was measured.

Clearly Filtered prints its challenge water as 50,000,000 with filtered water at under 1, in a column headed "CFU/L". That is a different unit from particles per milliliter, so its figure stays in its own unit when set beside the other three sheets. Keeping each count in the unit its sheet prints is what lets a comparison stay accurate.

Two results are closest to a like-for-like comparison when their rows share a size band, a challenge count in the same unit and the same kind of result label. When any of those differ, each percentage is best read as the outcome of its own test.

Reverse Osmosis at the Kitchen Sink

The data sheets above come from pitcher and countertop formats, and reverse osmosis also comes as an under-sink system that keeps the equipment below the counter. The CDC gives a reverse osmosis filter "a pore size of about 0.0001 micron" (CDC), which is 0.1 nanometer.

The Viomi M1 brings that format to a tankless under-sink system built around a 0.0001-micron precision membrane. The Viomi M1 removes 99%+ of microplastics, as well as lead, PFOS and PFOA, in independent testing by SGS. After the membrane, the Viomi M1 adds selected minerals back to the water used for drinking and cooking.

Households comparing several RO brands that target microplastics can find a brand-by-brand overview in RO water filter brands for microplastics.

What the Printed Fields Add Up To

Set side by side, a 96.48% average on 0.5 to under 1 micron particles and a 99.8% overall result on a pitcher cartridge are two separate tests, each tied to its own particle count, result label and cartridge. How microplastics end up in drinking water and bottled water in the first place is covered in microplastics in water and plastic bottles. Matching the part number on a replacement cartridge to the column that carries its result is the step that ties a printed percentage to the filter actually in use.

FAQ

Why do some data sheets list a particulate row and a microplastics row?

The two rows come from different standards. On the PUR pitcher sheet and the Brita Elite sheet, a particulate row sits under NSF/ANSI 42 and the microplastics row sits under NSF/ANSI 401. Each one is a separate claim with its own result, read from its own row.

Why is 85% printed on so many microplastics rows?

That figure is the minimum reduction the test requires. Brita's sheet marks it as the "NSF Minimum Percent Reduction Requirement", and AquaTru and PUR print it as "≥ 85%" and "≥85%". The filter's own result is printed in the neighboring column.

Can one cartridge carry certifications from more than one body?

The certification statements at the foot of a sheet show this. For the Brita Elite filter (OB06), the sheet credits WQA with certification against NSF/ANSI 42, 53 and 401, and separately credits IAPMO R&T with certifying the same filter against NSF/ANSI 53 for lead in a named list of Brita pitchers. The statement that mentions 401 is the one that covers the microplastics row.

Why do the Brita and AquaTru size bands use different wording?

Each sheet prints its own boundary notation. Brita writes "0.5-1 µm", while AquaTru writes "0.5 to < 1 µm", and the less-than sign places the upper edge just below 1 micron. The two bands sit close together, and each result stays with the band printed on its own row.