PFAS in tap water database (Japan)ExplainerChecked 2026.10.04
What happened in areas where high PFAS values were found in tap water? A timeline of Kibichuo, Tama, Okinawa and more
From FY2020 to the end of August 2025, 19 water supply operations exceeded the provisional target value of 50 ng/L. The highest was 1,400 ng/L in Kibichuo Town (吉備中央町), Okayama Prefecture. Using MLIT’s collection of response cases and local government releases, we build a timeline of what was found where and how it was dealt with.
Short answer
In the national table, 19 water supply operations exceeded 50 ng/L between FY2020 and the end of August 2025. As of December 2025, 18 had taken measures and their latest values were 50 or below, and 1 was under emergency response (the supplier’s name has not been disclosed).
The highest was 1,400 ng/L in the Enjo treatment plant (円城浄水場) system in Kibichuo Town, Okayama Prefecture (October 2022). It came to light in October 2023, and after about a month of drinking restrictions, the activated carbon was replaced and the water source changed; values were nd in FY2024 and FY2025.
Responses centered on three approaches: stopping high-concentration wells or sources, switching to other water, and adding activated carbon. In most documents, the cause has not been identified.
How many cases nationwide
- Number of operations exceeding 50 ng/L (national figure, by fiscal year): FY2020 11 → FY2021 5 → FY2022 4 → FY2023 3 → FY2024 (through end of September) 0. The cumulative total through the end of August 2025 is 19 operations.
- New exceedances in FY2024–FY2025 were Shimotsuke City (下野市), Tochigi (66, 63), Kizugawa City (木津川市), Kyoto (61, treatment plant outlet), Kobayashi City (小林市), Miyazaki (61), the Shiranui Tobu district small water supply system (不知火東部地区簡易水道) in Kumamoto (95), and the Tai small water supply association (田井簡易水道組合) in Hyogo (69).
- Of these, for Kizugawa, Kobayashi, Shiranui Tobu and the Tai association, as well as Fukuchiyama City (福知山市) and Seika Town (精華町) in Kyoto and Nishiwaki City (西脇市) in Hyogo, we could not confirm subsequent responses from official documents this time. Values can be seen in the tables on the prefecture pages.
- Within what we searched, we found no published cases of exceedances after the April 2026 water quality standard (we cannot say for certain there were none).
Timeline: areas where high values were found
From April 2020 to March 2026, 50 ng/L was a provisional target value (no obligation to test or comply). Values for raw water (water before treatment at the plant) are not tap water values.
| Period | Area, facility | Value (ng/L) | What followed |
|---|---|---|---|
| FY2015 | Okinawa Prefectural Enterprise Bureau, Chatan treatment plant | Treated water, fiscal-year max 120 | Before the provisional target value existed. FY2020 32, FY2021 35, FY2022 onward 5–13 |
| June 2020 | Kohama treatment plant (小浜浄水場), Takarazuka City (宝塚市), Hyogo | Raw water 55, tap 54 | Intake from two wells halved → intake stopped from August 2024 |
| July 2020 | Tokyo Metropolitan Waterworks Bureau, Ogawa water purification station (小川浄水所) (Kodaira City (小平市)) | Raw water 280, treated 68, tap 64 | High-concentration wells stopped. Tap 9 after the response |
| August 2020 | Kawaishinden water source (川合新田水源), Nagano City (長野市) | Tap 58 | Two of six wells stopped. Below the city’s own management standard of 25 ng/L (March 2021) |
| October 2020 | Osaka Water Supply Authority, Shijonawate water supply operation (四條畷水道事業), Tawara treatment plant (田原浄水場) | Tap 73 | Suspended on November 5, 2020 and switched to water from the bulk supplier. Raw water did not come down, so the plant was abolished at the end of FY2022 |
| November 2020 | Mitsui water source (三井水源地), Kakamigahara City (各務原市), Gifu | Raw water 99 | Fiscal-year max in the national table: 99 → 550 → 130 → 65 → 23 → 20 (sampling points mix tap, treatment plant outlet and raw water). Granular activated carbon installed in October 2023, bringing treated water to 50 or below |
| November 2020 | Enjo treatment plant, Kibichuo Town, Okayama | 800 | Response began only in October 2023 (section below) |
| FY2020 | Tado Chubu pumping station (多度中部送水場), Kuwana City (桑名市), Mie | Tap 290 | Pumping station stopped in October 2022, with water distributed from another distribution reservoir. nd from FY2023 |
| FY2020 onward | Akashigawa treatment plant (明石川浄水場) and Toba treatment plant (鳥羽浄水場), Akashi City (明石市), Hyogo | Exceeded in raw water (including river water from the Akashi River); treated water did not exceed | From FY2020, increased the share of groundwater and purchased water and strengthened activated carbon treatment. Plans to switch to water from the Hanshin Water Supply Authority (阪神水道企業団) from FY2025 and stop taking water from the Akashi River during FY2028 (November 2024 case collection) |
| March 2021 | Kitanagoya Water Supply Authority (北名古屋水道企業団), Toyoyama distribution reservoir (豊山配水場) system, Aichi | Raw water 175, treated 150 | Wells stopped and purchases from the bulk supplier increased |
| December 2021 | Okinawa Prefectural Enterprise Bureau, Chatan treatment plant | Raw water 75 | Increased low-concentration sources and dam water, and used granular activated carbon suited to adsorbing PFOS. Work on the intake weir (March 2024) |
| October 2022 | Kibichuo Town, Okayama | 1,400 | Highest value nationwide |
| October 2023 | Kibichuo Town, Okayama | Emergency testing 1,100–1,200 | Announced October 17; drinking restrictions (lifted November 22) |
| February 2025 | Ishibashi No. 2 distribution reservoir (石橋第2配水場), Shimotsuke City, Tochigi | National table 66 (FY2024), 63 (FY2025) | After guideline exceedances were found in wells in neighboring Utsunomiya City (宇都宮市) (November–December 2024), the prefecture and city were investigating groundwater in Shimotsuke when the city tested tap water from the Ishibashi No. 2 reservoir and found it exceeded the provisional target value. The city set up temporary water stations |
| December 25, 2025 | National follow-up survey | 19 operations | 18 had taken measures; 1 under emergency response |
Kibichuo Town: the highest case
- The Enjo treatment plant’s supply area covers 522 households, about 1,000 people, and draws water from the Kobira Dam (河平ダム). Fiscal-year highs in the national table were 800 (FY2020) → 1,200 → 1,400 → 1,100 (FY2023) → nd (FY2024 and FY2025).
- The public health center noticed it from the town’s response to the Japan Water Works Association’s “FY2022 Water Supply Statistics,” and contacted the town on October 13, 2023; the town announced it on October 17. The national table also shows 800 for FY2020, but the response began only after the October 2023 contact.
- The town distributed water by water truck and in plastic bottles, and lifted the drinking restriction on November 22, 2023. It changed the water source, cleaned the sedimentation basins, filter basins and distribution reservoirs, and replaced the activated carbon, and now supplies water from an agricultural dam and water bought from the regional water supply authority. According to town documents, it planned to complete facility work to buy all its water from the regional authority by March 2026.
- As of the town’s announcement, the cause is “unknown.” The town also accepts requests to test tap water at homes, and has posted survey results provided by the prefecture up to August 28, 2026.
- Figures from blood tests of town residents have been reported in the news, but we have not confirmed them in the town’s original documents, so we do not include them here.
Tama in Tokyo and Okinawa: what happened at large suppliers
- The Tokyo Metropolitan Waterworks Bureau found high values in some wells in Tama and stopped the high-concentration wells. The Fuchu Musashidai water purification station (府中武蔵台浄水所) had raw water at 420 and tap water at 41 in December 2020 and has been shut down since January 2021. In FY2025, 81 of the 84 tap sites in Tama were below 5 in every quarter; the highest was 14 in Mizuho Town (瑞穂町).
- In the national table, the Tokyo Metropolitan Waterworks Bureau’s value went from 64 in FY2020 to 11 in FY2025. Since it is one value for all of Tokyo, the reliable way to see your local value is the bureau’s tap-by-tap releases.
- The Okinawa Prefectural Enterprise Bureau’s Chatan treatment plant supplies water to Chatan Town (北谷町), Okinawa City (沖縄市), Ginowan City (宜野湾市), Urasoe City (浦添市), Naha City (那覇市) and others. Its source, the Hija River (比謝川), still had a maximum of 143 in FY2025, but treated water has had fiscal-year highs of 5–13 since FY2022. The bureau publishes values by source weekly to monthly.
Private water supplies at Self-Defense Force bases, hospitals and other facilities
- Among in-house water systems (private water supplies) for company housing, hospitals, schools, bases and so on, 59 of the 4,353 tested exceeded 50 (FY2020 to the end of August 2025). By prefecture, Tokyo had the most, at 22.
- Among private water supplies set up by the national government, the highest was 1,500 ng/L at the Japan Air Self-Defense Force’s Ashiya Air Base (芦屋基地) (Fukuoka); it reportedly stopped the high-concentration wells, is responding temporarily with water filters, and plans to switch to the municipal water supply. Values such as 560 at Nyutabaru Air Base (新田原基地) (Miyazaki) and 245 at Fuchu Air Base (府中基地) (Tokyo) are raw water values.
- Values for private water supplies are for water used within that facility, not the tap water of the surrounding area.
Types of response, and what changes from April 2026
Based on past cases, MLIT produced a “Manual for responding to PFOS and PFOA for water suppliers.”
| Stage | Main measures | Examples |
|---|---|---|
| Emergency | Switching or blending water sources, replacing activated carbon, powdered activated carbon, drinking restrictions and emergency water supply | Kibichuo, Shijonawate, Shimotsuke |
| Medium term | New wells, facilities to receive purchased water, granular activated carbon or ion exchange facilities | Kakamigahara, Kitanagoya, Kuwana |
| Long term | Abolishing water sources, switching to water from another supplier | Shijonawate (abolition of the Tawara plant), Akashi |
- From April 2026, it is a water quality standard, and if it is exceeded, suppliers immediately investigate the cause and take steps to lower the concentration.
- Assessments of health effects are covered in the guide to health, and the relationship between high values in rivers and groundwater and tap water in the guide to the environment.
Sources
- MLIT, “PFOS and PFOA response cases by water suppliers to date” (November 29, 2024)
- Ministry of the Environment, results of the follow-up survey (December 25, 2025)
- Ministry of the Environment, survey results (final compilation, including private water supplies, December 24, 2024)
- Kibichuo Town, “Detection of organic fluorine compounds and other substances at the Enjo treatment plant”
- Tochigi Prefecture, “Exceedance of the provisional guideline value for PFOS and PFOA in groundwater in Shimokoyama, Shimotsuke City (2nd report)”
- Okinawa Prefectural Enterprise Bureau, detection status of PFOS and related substances
- Tokyo Metropolitan Waterworks Bureau, PFOS/PFOA and related measurement results in the Tama area (FY2025)
- MLIT, “Manual for responding to PFOS and PFOA for water suppliers”
Last checked 2026.10.04 (against the original government documents and papers, collected and cross-checked in Gemini Notebook). Utility values are as in the national table; Urayomi sorted and summarized them.
This page lists levels published by national and local government bodies and facts from standards, assessments and papers. It does not judge whether tap water is good or bad or whether it affects health. Check the latest values and measures with your local water utility.