Tap water, bottled water, water filters and microplastics
How much treatment plants remove, studies of bottled water and their critics, and filter certification
In short
Coagulation, sedimentation and filtration at water treatment plants remove most microplastics (about 99.9% in an experiment, and 97% at a Geneva plant). WHO says there are no data showing a clear health concern for drinking water.
Japan's drinking water quality standards have no item for microplastics. We also found no national survey of Japanese tap water.
Tap water
- How much treatment plants remove: In an experiment at Hokkaido University, coagulation, sedimentation and rapid filtration removed 2.9 log (about 99.9%), about the same as clay particles (Nakazawa et al. 2021). At a Geneva treatment plant, raw water had 25.7–55.6 particles per m³ and treated water had 0–4 (97%, particles of 0.063 mm or larger).
- Smaller particles are harder to remove: Coagulation and sedimentation alone removed less than 2% to 13.6%, and filtration 86.9–99.9%. Sand filtration stopped particles over 0.02 mm completely, but about 16% of 0.01 mm particles got through (studies from 2020 and 2021). WHO says conventional treatment optimized to lower turbidity can also remove particles smaller than 1 μm.
- After the water leaves the plant: A study by Tokyo University of Science (42 samples from 5 countries, an average of 39 particles per liter) says PVC fragments larger than 0.05 mm may have come from water pipes and the like (→ Tap water).
- Japan's standards: Microplastics are not among the 52 water quality standard items or the 26 water quality management target items (Ministry of the Environment list).
- Other countries: California defined microplastics in drinking water (2020) and plans to start testing treated water in autumn 2026. The EU set a measurement method (2024). In 2026 the US EPA did not include microplastics in its national monitoring, citing the lack of a validated analytical method (→ Rules and regulation).
Bottled water
- The finding of “about 240,000 particles per liter, about 90% of them nanoplastics” (Qian et al. 2024, PNAS) has drawn criticism of how the blanks were handled, and a rebuttal from the authors.
- The ranking by container type changes from study to study, and one study found more in glass bottles (→ Bottled water, Drinks in glass bottles).
Household water filters
- Comparison of pour-through (pitcher) types (Cherian et al. 2023): 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 that came out sometimes had more particles than the water that went in.
- US certification NSF/ANSI 401: An item for “microplastics reduction” was added in 2021. The condition is a reduction of at least 85% of particles of 0.5–1 μm. However, the particles used in the test are mineral test dust, not plastic itself (explanation by an NSF representative). You can check certified products in the NSF list.
- Japanese standards: Microplastics are not among the substances to be removed under the JIS standard for household water purifiers (S 3201) or among those that may be labeled under the Household Goods Quality Labeling Act. We found no example of a domestic manufacturer publishing a microplastic removal rate.
What about boiling tap water?
In a Chinese study (Yu et al. 2024), when hard water (over 120 mg of calcium carbonate per liter) was boiled, polystyrene, polyethylene and polypropylene particles of 0.0001–0.15 mm were trapped in the calcium carbonate crystals that formed, and over 80% were removed. Japan's water quality management target for hardness is 10–100 mg/L, and this study does not show whether the same reduction occurs in soft water, which is low in calcium.
Sources
- WHO, “Microplastics in drinking-water”, 2019
- Ministry of the Environment: drinking water quality standards and water quality management target items (Japanese)
- Nakazawa Y et al. Water Res 2021;203:117550
- Negrete Velasco A et al. 2023
- Zhang et al. 2020 (coagulation-sedimentation and filtration)
- Na SH et al. 2021 (sand filtration)
- Mukotaka A et al. Sci Total Environ 2021;790:148231
- Kosuth M et al. PLoS One 2018
- Qian N et al. PNAS 2024
- Materić D et al. PNAS 2024 (letter)
- Cherian AG et al. Polymers 2023;15:1331
- Yu Z et al. Environ Sci Technol Lett 2024
- Water Conditioning & Purification Magazine, “Microplastics reduction testing”, September 2021 (explanation by an NSF representative)
- NSF certified products list (household water filters)
- California State Water Resources Control Board, “Microplastics in Drinking Water”
Last checked 2026-10-01. Research and regulations change over time. This page is a translation of our Japanese page; if they differ, the Japanese page is the reference.