Methodology
How We Test Your Water
Our process is based on fluorescence microscopy protocols used by the EPA, NOAA, and NIST for environmental microplastic detection.
Sample Collection
Each participant receives sterile borosilicate glass vials with PTFE-lined caps — no plastic touches the sample at any point. Vials are pre-cleaned and sealed in our lab.
Participants collect 100ml of tap water directly from their faucet after running it for 30 seconds to clear standing water from the fixture. Samples are mailed back in a prepaid mailer within 48 hours of collection.
Vacuum Filtration
The full 100ml sample is vacuum-filtered through a 0.45μm cellulose nitrate membrane. This pore size captures microplastic particles down to the sub-micron range while allowing dissolved minerals and organic matter to pass through.
The membrane retains all solid particles from the sample on its surface, concentrating them into a small area for imaging.
Nile Red Staining
The filter membrane is stained with Nile Red, a lipophilic fluorescent dye that selectively binds to synthetic polymers (plastics). Nile Red has been widely validated for microplastic detection in peer-reviewed literature.
When excited at the proper wavelength, plastic particles fluoresce bright orange while non-plastic particles (minerals, sediment, organic matter) remain dark or show minimal fluorescence. This makes plastic unmistakable in the final image.
Fluorescence Imaging
The stained membrane is imaged under a fluorescence microscope using a blue excitation filter (450–490nm) and an orange emission filter (520nm+). This combination maximizes the contrast between fluorescing plastic particles and the dark background.
We capture high-resolution images at standardized magnification so every sample is directly comparable. The resulting image shows every microplastic particle as a bright orange dot or fragment against a black field.
Counting & Classification
Particles are counted manually from the fluorescence image. Each bright particle that meets the fluorescence intensity threshold is counted as a suspected microplastic. Results are reported as particles per 100ml.
We classify results into three tiers based on particle count: Low (0–5 particles), Moderate (6–15 particles), and High (16+ particles). There is currently no federal safety standard for microplastics in drinking water, so these tiers are relative benchmarks based on our dataset.
Quality Control
- ✓Blank controls — We regularly run blank samples (purified water through the same process) to verify our equipment and environment aren't introducing contamination.
- ✓Glass-only contact — Samples only touch borosilicate glass and PTFE. No plastic containers, no plastic tubing, no plastic filtration housings.
- ✓Standardized imaging — Every sample is photographed at the same magnification, exposure, and filter settings for consistent, comparable results.
- ✓Open results — All data is published on the map. Nothing is cherry-picked or withheld.
Limitations
Fluorescence microscopy with Nile Red is a screening method, not a definitive identification. While it reliably detects synthetic polymers, some organic particles may exhibit weak fluorescence. For definitive polymer identification, techniques like FTIR or Raman spectroscopy would be required.
Our particle counts represent what is present in a single 100ml sample at a specific point in time. Water quality can vary by time of day, season, and plumbing conditions. Results are specific to the sample provided.
Protocol References
- • EPA Method 8272 — Microplastics in environmental samples
- • NOAA Marine Debris Program — Laboratory methods for the analysis of microplastics in the marine environment
- • NIST Reference Materials — Standards for microplastic particle characterization
- • Maes et al. (2017) — “A rapid-screening approach to detect and quantify microplastics based on fluorescent tagging with Nile Red”
- • Shim et al. (2016) — “Identification and quantification of microplastics using Nile Red staining”