Microplastics in tap water
Tap water surveys vary widely depending on the size of the particles counted and the identification method, and a 2025 analysis pooling 43 studies says “comparison between studies is not reliable.” In water treatment plants, coagulation, sedimentation and filtration removed around 99.9% in experiments.
Amounts found in studies
| Study | What was tested | Size range and method | Results |
|---|---|---|---|
| Kosuth et al. (2018) | 159 samples from 14 countries (none from Japan) | 0.0025 mm filter, stained and counted visually (no identification by spectroscopy) | Artificial particles in 81%. Average of 5.45 particles per L, 98.3% of them fibers |
| Mukotaka et al. (2021, Tokyo University of Science) | 42 samples from 5 countries | FTIR (0.019 mm and larger) | 1.9–225 particles per L, average 39. PVC fragments over 0.05 mm may have been introduced after leaving the treatment plant (water pipes, etc.) |
| Malekzadeh et al. (2025) | Meta-analysis of 43 studies | Varies by study | Average of 56.98 particles per L. With no unified procedure, comparison is “not reliable” |
| Nakazawa et al. (2021, Hokkaido University) | Water treatment experiment | — (confirmed in the abstract) | Coagulation, sedimentation and rapid filtration removed 2.9 log (about 99.9%). About the same as clay particles |
| Negrete Velasco et al. (2023) | A water treatment plant in Geneva | 0.063 mm and larger | Raw water 25.7–55.6 particles per m³ → treated water 0–4 (97% removal) |
Results can differ by orders of magnitude depending on the smallest particle size counted and whether particles are counted or weighed. Numbers from different studies cannot be compared directly (→ Why numbers differ).
Good to know
- WHO (2019) says “conventional water treatment can remove particles smaller than 1 μm” and “from the limited information available, microplastics in drinking water at current concentrations do not appear to pose a health risk.”
- Sand filtration completely stopped particles over 0.02 mm, but about 16% of 0.01 mm particles passed through (Na et al. 2021). The smaller the particle, the harder it is to remove.
- Kosuth 2018 was a project of the news organization Orb Media and did not identify particles by spectroscopy (stated in the paper).
What you can do at home (shown in research)
- A study comparing pour-through household water filters found that models with a membrane (MF) removed 78–86% of PVC and 94–100% of PET, and the model with a 0.2 μm membrane removed the most. With models using only activated carbon and ion exchange, the water coming out sometimes had more particles than the water going in (Cherian et al. 2023).
- One study found that boiling hard water (over 120 mg per L as calcium carbonate) forms calcium carbonate crystals that trap 0.0001–0.15 mm polystyrene, polyethylene and polypropylene, removing more than 80% (Yu et al. 2024). The water quality management target for tap water in Japan is a hardness of 10–100 mg/L, and this study did not show the effect in soft water.
Data from Japan
There are studies from Tokyo University of Science and Hokkaido University. We found no official survey in which the national government or a local government measured Japanese tap water (the tap water quality standards have no item for microplastics).
Types of plastic found
Related explainers
Sources
- Kosuth M, et al. PLoS One 2018;13:e0194970 (PMID 29641556)
- Mukotaka A, et al. Sci Total Environ 2021;790:148231 (PMID 34380239)
- Malekzadeh, et al. Ecotoxicol Environ Saf 2025;299:118347 (PMID 40393317)
- Nakazawa Y, et al. Water Res 2021;203:117550 (PMID 34418646)
- Negrete Velasco A, et al. 2023 (PMID 37023809)
- Na SH, et al. 2021 (PMID 34271456)
- Cherian AG, et al. Polymers 2023;15:1331 (PMID 36987112)
- Yu Z, et al. Environ Sci Technol Lett 2024 (boiled tap water)
- WHO, “Microplastics in drinking-water,” 2019
Last checked 2026-10-01. “Confirmed in the abstract” means we report only what the paper's abstract says. This page is a translation of our Japanese page; if they differ, the Japanese page is the reference.