Our microplastics test kit, explained

You run it on your counter, no lab and no mailing anything away. Stain a 100 mL sample, push it through a filter, then look at the filter under the digital microscope. Plastic shows up as bright pink particles — you read the result yourself, live under the microscope, in minutes.

1. Collect your sample in a clean glass container (not plastic, so the container can't shed plastic into your test). Rinse it three times with the same water you're testing, then fill to ~100 mL.

2. Add the digestion solution. It breaks down algae, biofilm, and organic gunk that would otherwise cloud the result. Wait ~30 minutes.

3. Add the Nile Red stain. The dye latches onto hydrophobic (water-repelling) particles, which is nearly all common plastics. It physically can't bind to minerals, salts, or dissolved solids. Wait 30–60 minutes.

4. Filter the sample. Push the stained water through the membrane filter, which traps everything the dye grabbed.

5. Look at the filter under the digital microscope. Particles consistent with microplastics glow bright pink against the membrane.

6. Read and interpret the result yourself. Under the microscope you see and count the bright pink particles live, then compare against your second test to see how your water stacks up.

7. Run the second test on another source and compare. Tap vs. your filter's output, same day, same handling — the difference is what tells you whether your filter is doing anything.

Nile Red is a fluorescent dye that binds to hydrophobic surfaces and lights up under blue light. Because plastics are hydrophobic, it's a well-established way to make microplastics visible without a $25,000 instrument.

The staining approach is peer-reviewed: it was validated by Maes et al. in 2017 and used in the 2018 survey that tested 259 bottles across 11 brands in 9 countries and found microplastics in 93% of them, averaging 325 particles per liter. We built an at-home kit around that science so you can see the result for $75 in about 15 minutes, instead of shipping a sample to a $600 lab.

Be clear about what a count is: it's suspected microplastic — hydrophobic particles caught on the filter and stained. It is not a chemically confirmed plastic ID. That takes spectroscopy (micro-FTIR, Raman) or pyrolysis GC/MS. This is a screening test, and we say so out loud.

Counting particles from ~1 µm up to ~5 mm: bottle-wall fragments, pipe-shed flakes, packaging films, and synthetic fibers (polyester, nylon, acrylic). At that size class, an at-home Nile Red kit and a lab running the same protocol land on comparable counts. That's the entire point of using a standardized, published method.

Side-by-side comparisons, which is where it shines. Run tap vs. your filter's output, or a fresh bottle vs. one that sat in a hot car, on the same day with the same handling. The difference between two counts is far more trustworthy than any single absolute number, and it's the question most people actually have: is this thing I bought doing anything?

Repeatability lands within about ±15% run to run — normal for particle counting. Because the stained particles glow bright pink against a clean membrane, they're easy to pick out consistently under the microscope.

It can't see nanoplastics under 1 µm. The filter pore is the floor. This is the size class that matters most for the body, because sub-micron particles cross cell membranes and the gut lining — and it's invisible to any optical consumer kit, ours included.

It can't tell you the polymer. PE vs. PET vs. PVC needs lab spectroscopy. The kit confirms presence and quantity; a lab adds the chemical identity.

It can give false positives. Nile Red stains hydrophobic material generally, so lipids, waxes, rubber, and organic-rich samples (tea, formula, old-plumbing biofilm) can fluoresce too. On those samples, read your count as an upper bound. The lab fix is a hydrogen-peroxide digestion step; we ship without digestion-strength peroxide because it's hazardous to mail, so this is a rapid, safe screen — not a lab assay. We don't publish a single false-positive percentage yet; a spike-recovery study is in progress, and we'd rather say that than invent a number.

The honest edge of any at-home test is the membrane itself. Filter membranes come from different vendors and vary batch to batch — some carry a little trace material of their own, and it's genuinely hard to QA an individual membrane before it ships. Across the 250+ tests we've run since inception we've learned which suppliers run cleanest, and we're continually moving to higher-quality filters with lower background.

Because a membrane can carry a small baseline, treat any single count as an upper bound, not an exact number.

Here's how to sharpen it yourself: before you run your sample, look at an unused filter under the digital microscope and do a rough count of any dots already glowing on it. Then run your water, count again, and subtract that baseline. A formal procedural blank — clean water through the whole workflow — is the lab version of the same move, but this quick visual check gets you most of the way there. And the two-tests-per-kit design does it for you automatically: the membrane baseline hits both samples equally, so the difference between them stays clean.

The kit tests a 100 mL glass, so it helps to bring the giant per-liter study numbers down to that scale — as a reference, not a promise.

The 2018 bottled-water survey (Mason et al.) averaged 325 particles per liter, which divides arithmetically to about 33 in a 100 mL glass: roughly 1 particle above 100 µm and about 31 in the 6.5–100 µm range. One nuance that matters — the study's imaging only reliably counted down to ~6.5 µm even though its filters caught finer debris, so 325/L is an above-that-size figure and the real number is higher.

Treat that ~33 as a theoretical conversion, not a prediction of your result. It's a study average sliced into a smaller glass; a real count swings widely with brand, bottle age, storage temperature, and handling, and no single test 'should' hit the average. Because our kit resolves down to ~1 µm — finer than that 2018 counting floor — a plastic-heavy bottle could read higher, or a clean source lower. Rough kit reference points: distilled water comes back with only a few particles, typical tap runs on the order of 10–100, bottled water is often higher.

Below all of it sits the nanoplastic range no optical kit reaches. The 2024 study from Columbia (Qian et al., PNAS) used stimulated Raman scattering to image particles down to ~100 nm and found, on average, about 240,000 plastic particles per liter across three popular bottled brands — roughly 90% of them nanoplastics, and 10–100x more than the older micron-scale surveys. All seven common plastics showed up; the most abundant was polyamide (a nylon often used in water-filtration membranes), followed by PET, the plastic bottles are made of. Those particles are real, but invisible to Nile Red or any consumer kit. Your micron count is the visible proxy for that larger, unseen load.

Every microplastics test has these limits — the expensive labs included. Most just don't write them down for you. We did, on this page, because the whole promise of the kit is that you get to see the evidence with your own eyes instead of taking a number on faith.

So here's the deal, plainly: it's a $75 at-home kit with two tests inside, it shows you plastic down to ~1 µm in about 15 minutes, it's the same chemistry the published studies used, and it won't catch nanoplastics or tell you the polymer. If that's the honest answer you wanted, run it — and compare two sources so your result stands on its own.