Bottom line: Nanoplastics — plastic particles under 1 micron — slip through most home water filters. Sub-micron hollow-fiber pitchers stop at 0.2μm; only reverse osmosis (~0.0001μm pore size) is fine enough to physically block the nanoplastic fraction.

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Why Nanoplastics Are Different

Microplastics are particles 1μm–5mm. Nanoplastics are smaller than 1μm, often hundreds of times smaller — and a 2024 study using new detection methods found that 90% of plastic particles in bottled water were nanoplastics, not microplastics1. That changes the filter conversation entirely.

Filter type Pore size Catches nanoplastics?
Brita / PUR / standard pitcher Activated carbon (no fixed pore) No
LifeStraw Home pitcher 0.2μm No (catches >0.2μm only)
Standard under-sink carbon block 0.5–5μm No
Reverse osmosis ~0.0001μm Yes (>99% removal)
Distillation Phase change Yes (but slow, energy-intensive)

A 0.2-micron hollow-fiber filter is fine enough for bacteria and microplastics but 2,000× too coarse for the smallest nanoplastic fragments. RO is the only widely-available home technology that handles nanoplastics.

What You Can Do

  1. Use reverse osmosis for drinking water. AquaTru Countertop RO (no install) or Waterdrop G3P800 under-sink RO (built-in) — both have the 0.0001μm membrane required. Compared in our best water filter for microplastics guide.
  2. Stop drinking bottled water. Bottled water averages twice the microplastic load of tap, and the 2024 nanoplastic study found ~240,000 plastic particles per liter — most of them nanoplastics shed from the bottle itself.
  3. Don’t rely on pitcher filters for the nanoplastic claim. A pitcher is fine for the larger microplastic fraction, but it won’t touch nanoplastics. If nanoplastics are why you’re filtering, skip the pitcher and go straight to RO.

Frequently Asked Questions

What's the smallest particle a water filter can catch?
Reverse osmosis membranes block particles down to roughly 0.0001 microns (0.1 nanometers), which is small enough to catch nearly all nanoplastic fragments. Sub-micron hollow-fiber filters stop at about 0.2 microns — fine for microplastics, but they let smaller nanoplastics through.
Does LifeStraw remove nanoplastics?
Not the nanoplastic fraction. LifeStraw’s 0.2-micron hollow-fiber membrane blocks particles larger than 0.2μm — that includes microplastics, bacteria, and parasites, but most nanoplastics are smaller than that cutoff. For nanoplastics specifically, reverse osmosis is the home solution.
Why are nanoplastics worse than microplastics?
Their size lets them cross biological barriers that microplastics can’t — including the gut wall, the blood-brain barrier, and into individual cells. The 2025 Nature Medicine study finding plastic particles in human brain tissue measured most particles in the nanoplastic range. See our brief on microplastics in the brain.

For the full comparison of microplastic and nanoplastic-rated filters, see our best water filter for microplastics guide.

This article is for informational purposes only and does not constitute medical advice.

  1. Qian, N., Gao, X., Lang, X., et al. “Rapid single-particle chemical imaging of nanoplastics by SRS microscopy.” PNAS, Volume 121, Issue 3, 2024. DOI ↩︎