How It Works
How You Test Your Water
The kit uses Nile Red fluorescence staining — developed in academic labs and validated in peer-reviewed research. We didn't invent this science. We packaged it so anyone can run it in the home.
Based on: Leonard et al., “Smartphone-enabled rapid quantification of microplastics,” Journal of Hazardous Materials Letters, 2022. DOI: 10.1016/j.hazl.2022.100052
Collect your water samples
Use any glass container you have at home — a mason jar, a drinking glass, anything clean. Glass, not plastic — so the container can't shed plastic into what you're testing. Fill it with about 100 mL. Run two samples so you can compare any two sources side-by-side — that takes two tests, sold separately from the kit.
Drop in the Nile Red vial
Drop in the single Nile Red vial — the fluorescent dye — and wait. Fifteen minutes is the minimum; longer is fine, and actually better. The dye binds to hydrophobic (water-repelling) particles, which includes virtually all common plastics. It physically cannot bind to minerals, salts, or dissolved solids — that's chemistry, not a design choice. But it isn't plastic-exclusive: some non-plastic hydrophobic material (waxes, lipids, rubber) can also pick up the stain, which is why we call this a screening count rather than a definitive plastic ID.
Filter your sample
Push the stained water through the included filter using the syringe. The filter traps everything the dye attached to while the water passes through.
Look under the microscope
Place the filter under the included digital microscope. The stained microplastics show up as bright pink particles against the filter background — you read the result yourself, live under the microscope, in minutes.
Count the particles
Count the bright pink particles on the filter under the microscope and note how big they are. That count is your result — you interpret it yourself, no photo to upload and no report to wait for.
Compare and interpret
More pink specks = more potential microplastics. Run the second test with filtered water and compare side-by-side under the microscope. The difference tells you whether your filter is actually working.
What You Get
- Bright pink particles on your filter, right under the included digital microscope
- Clear before/after comparison if you test tap vs. filtered water
- A particle count and rough size you read yourself under the microscope, live, in minutes
- See how your water compares to other homes on The Water Map
What We Detect
- Microplastic particles ≥10 µm (width of a red blood cell)
- All common polymers: polyethylene, polypropylene, nylon, PET, polystyrene
- Fibers, fragments, and films
What We Don't
- Nanoplastics (<10 µm) — no consumer test does this
- Exact polymer ID (PE vs PP) — that's the $800 test
- Certain hydrophilic plastics (rare in drinking water)
- Definitive plastic ID — Nile Red is a screening stain; rare non-plastic hydrophobic particles can also glow
We're transparent about this because no test is perfect. The $800+ FTIR/Raman tests can identify polymer types, but they detect the same size range of particles. The question is whether you need an $800 answer or a $75 one you can run in the home. Every limitation of this test — false positives, contamination, detection floor — is documented in full on the limitations page.
Quality Controls
Contamination control in the home
The biggest error source in any microplastic test — lab or home — is contamination from the surrounding environment: airborne fibers settling into an open container, dust on a jar that's been sitting out. The protocol's defenses are simple: keep the jar covered while you wait, and filter promptly.
Side-by-side comparison design
Run two samples rather than one. Same day, same room, same handling — tap vs. filtered, tap vs. bottled — and ambient contamination hits both samples roughly equally. The difference between the two counts is far more robust than any single absolute number. Tests are sold separately, so order at least two if you want the comparison.
Locked protocol
Every kit follows the same standardized procedure. Same reagent concentrations, same timing, same filter, same microscope setup. Consistency is how results stay comparable across thousands of tests.
Glass-only contact
Samples only touch glass and non-plastic materials. No plastic containers, no plastic tubing. The container can't shed plastic into the sample.
Every sample public
Every test result and its raw image gets posted to the public map. Anyone can look at a sample and tell us if something looks wrong.
Procedural blank baseline
We run clean, filtered water through the entire process — same vials, same filter, same microscope — and it consistently returns 0–3 particles on the filter. That's the floor the procedure itself can introduce; anything meaningfully above it is real.
Filter membranes & how to sharpen your count
The honest edge of an in-home test is the filter membrane itself. Membranes come from different vendors and their quality varies batch to batch — some carry a little trace material of their own, and it's hard to QA an individual membrane before it ships. Across the 250+ tests we've run since inception we've learned which suppliers produce the cleanest membranes, and we're continually working to move to higher-quality filters with lower background. Treat any single count as an upper bound, not an exact number.
You can account for the membrane's baseline yourself with a quick blank: before you run your sample, look at an unused filter under the digital microscope and do a rough count of any glowing dots already on it, then run your water, count again, and subtract the first number. A formal procedural blank is the lab version of the same idea — the quick visual check gets you most of the way there. Running the two included tests side-by-side does this for you too: the membrane baseline hits both samples equally, so the difference between them is the trustworthy signal.
Want the unvarnished version — false positives, contamination, detection floor, in QA/QC language? It's all on the limitations page.
Validation Roadmap
We don't claim to be done. We claim to be transparent about what we're testing right now. Big lab companies tell you everything is finished. We're showing you the work in progress, because the work is the trust.
Peer-reviewed detection method
Nile Red fluorescence imaging, based on the protocol described in Leonard et al. 2022 (Journal of Hazardous Materials Letters). We adapted the published method — we didn't invent it, and we're not affiliated with the authors.
Spike-recovery calibration curve
Running known concentrations of polyethylene reference particles (0, 10, 100, 1,000 per 100 mL) through the kit pipeline to publish a kit-vs-known regression line and an honest error bar. Every result we publish gets a defensible confidence interval once this lands.
Independent split-sample comparison
We want to run our pipeline against an ELAP-accredited FTIR/Raman lab on the same source water, and publish the chart — even if it makes us look bad. We have not lined up a partner lab yet.
Cross-kit reproducibility study
Five users running the same spiked standard through five different kits. If counts diverge by more than 2x, the kit isn't ready and we'll say so.
Open-source the counting code
Our YOLO-based particle counting model will be published on GitHub. Anyone can download it, audit it, run it on their own images, and tell us where it's wrong.
Want to verify any of this independently? Every public test result and the full underlying dataset is on thewatermap.com — free, open, no paywall, no signup.
The Paper We Cite
In 2022, Leonard et al. published a peer-reviewed paper in the Journal of Hazardous Materials Letters describing Nile Red fluorescence imaging for microplastic detection. Their reported method reliably detected and quantified microplastics as small as 10 µm (one-tenth the width of a human hair) across all common polymer types. That is the method we adapted for this kit.
To be explicit: the authors and their institution have not endorsed, reviewed, or validated this kit. We cite their paper because that's where the protocol comes from.
Leonard, J., Koydemir, H.C., Koutnik, V.S., Tseng, D., Ozcan, A., & Mohanty, S.K. (2022). “Smartphone-enabled rapid quantification of microplastics.” Journal of Hazardous Materials Letters, 3, 100052. DOI: 10.1016/j.hazl.2022.100052
Why This Matters Now
Microplastics have been found in:
- Arterial plaqueof heart patients — New England Journal of Medicine, March 2024
- Human blood, liver, kidneys, and placenta— multiple studies, 2022–2025
- Breast milk and infant meconium— meaning babies are exposed before birth
- Cerebral blood vessels— a 2025 Science Advances study linked bloodstream microplastics to thrombosis
California SB 1422 requires major utilities to test treated tap water starting Fall 2026.
New Jersey, Virginia, and Illinois have passed similar laws. The science is moving faster than the regulation. We think you shouldn't have to wait for the government to tell you what's in your water.
Results are provided for informational purposes and should not be interpreted as a regulatory or health determination. Data reflects individual household samples and may not represent municipal water system conditions.