How to know if your water has microplastics

The size class called “microplastic” runs from 1 µm to 5 mm. The fraction in drinking water is almost entirely at the small end. A 2018 Orb Media / State University of New York Fredonia survey counted particles down to 6.5 µm in bottled water and found about 325 of them per liter on average across 11 brands. A 2024 PNAS paper out of Columbia and Rutgers pushed the resolution down to ~100 nm and found roughly 240,000 particles per liter in bottled water, with about 90% in the nanoplastic range.

You will never see any of that. A human hair is 70 µm wide. A grain of fine table salt is 100 µm. Most of what's in your glass is below both.

If your tap pours cloudy and the cloud clears from the bottom up over 30 seconds, that's dissolved air. Common in winter when cold water hits the warmer pressurized line. Not plastic.

If the cloudiness stays, settles to the bottom as white scale, or leaves rings in a kettle, that's calcium carbonate. A symptom of hardness, not contamination.

If the water is faintly yellow or brown, that's iron oxide or tannins from organic matter. Annoying, but not microplastic.

A glass of water can be visually perfect and still carry tens of thousands of plastic particles per liter. Visual inspection is the one thing that can't tell you what you want to know.

A swimming-pool smell is chlorine or chloramine, used by every US utility. A rotten-egg smell is hydrogen sulfide, usually from a water heater or a well. A metallic taste is iron, copper, or lead (test for lead separately if a metallic taste is new). None of these correlate with plastic load.

Microplastic particles don't taste like anything. Polyethylene and PET in particular are flavorless, odorless, and chemically stable. Your tongue is the wrong instrument.

You filter a known volume of water through a membrane fine enough to trap particles down to about 1 µm. You add a fluorescent dye called Nile Red that binds to plastic polymers and almost nothing else. You shine 450nm blue light at the membrane. Plastic glows pink. You count the dots.

That's the protocol. It's what university labs use, what the Orb Media study used, and what the at-home kit on this site ($50, two tests, 15 minutes per sample) packages so a normal person can run it on a kitchen table. You can read the full step-by-step in how to test water for microplastics at home.

The kit will not tell you which polymer you're looking at (that's a five-figure py-GC/MS instrument) and it will not catch particles smaller than 1 µm. It will tell you how many microplastic-sized particles are in a glass of your water, how that compares to a blank, and how it compares to a sample from after your filter.

If you only test one thing, test cold tap water from the kitchen first thing in the morning. That's the water that's been sitting in your home's pipes overnight and picked up whatever they shed. It's the highest-particle sample you can take.

A second worth running is the output of whatever filter you trust — pitcher, faucet mount, reverse osmosis, whole-house. That tells you whether the filter is actually doing anything for plastic. Manufacturer claims and independent teardowns rarely agree.

A third is whichever bottled or boiled water you switch to when you don't trust the tap. People are often surprised to find their “safe” option is dirtier than the one they were avoiding.