PFAS in tap water: Okinawa Prefecture

Levels by utility (PFOS + PFOA combined, ng/L)

These are the highest values in each fiscal year reported by each utility to the national government (MLIT and the Ministry of the Environment). A utility with several sources or treatment plants can have different levels in different parts of its area. Samples are taken at the tap in principle, but some utilities only measured raw water (water before treatment), and raw-water values are not covered by the tap-water standard. nd = below the detection or quantification limit; — = no value reported. *FY2025 covers results up to the end of August 2025. Utility names are left in Japanese as in the official table.

>50 a year above 50 ng/L (for utilities that also sampled raw water, the value may be from raw water)　raw above 50 ng/L, but measured in raw water only

Values published by local governments and utilities

Good to know

• Of the prefecture’s 41 rows, 21 “buy all their water” (they have no water source of their own and buy water), including Naha City (那覇市), Okinawa City (沖縄市), Ginowan City (宜野湾市), Urasoe City (浦添市) and Uruma City (うるま市). According to the Enterprise Bureau, water from the Chatan treatment plant (北谷浄水場) goes to Chatan Town (北谷町), Okinawa City, Kitanakagusuku Village (北中城村), Nakagusuku Village (中城村), Ginowan City, Urasoe City and Naha City, and water from the Ishikawa (石川), Nishihara (西原) and Nago (名護) treatment plants also goes to their respective cities, towns and villages. Which water goes to which part of a city, town or village is decided by each municipality’s water service. → How can I check PFAS in the tap water where I live?
• Separately from the national survey, the Okinawa Prefectural Enterprise Bureau measures the Chatan treatment plant’s water sources (the Hija River (比謝川), Nagata River (長田川), Tengan River (天願川) and Kadena well field (嘉手納井戸群)) and the plant’s inlet and outlet once a week to once a month, and publishes the results. In FY2026 (April 1–August 28), the Chatan treatment plant outlet had a maximum of 6 and an average of 4 ng/L (22 tests), and the Nago, Ishikawa and Nishihara treatment plants were below 1 at both inlet and outlet.
• The Enterprise Bureau’s values in the national table (32 in FY2020, 35 in FY2021, 6 in FY2022, 5 in FY2023) match the fiscal-year maximums for treated water at the Chatan treatment plant published by the Enterprise Bureau. For FY2024 and FY2025, the national table shows 5, while the Enterprise Bureau’s fiscal-year totals show 6 and 13 (the FY2025 figure covers the full fiscal year); the differences come from cutoff dates and counting methods.
• The Hija River, a water source for the Chatan treatment plant, continues to show high values even though intake from it has been stopped (FY2025 maximum 143; FY2026 April–August maximum 165). In FY2026 (through the end of August), the Chatan treatment plant’s intake was 73.4% dam water and other sources, 9.6% seawater desalination, 9.2% the Kadena well field and 7.8% the Nagata River; no water was taken from the Hija or Tengan rivers.
• Kin Town’s values were 70→59→41→2→nd→nd (FY2020→FY2025). According to an MLIT collection of case studies, the exceedance was found in raw water (water before treatment; Kin Sources No. 1–6 (金武1〜6号水源) and Warumibaru Source No. 1 (和留美原水源1号)). After limiting and stopping intake and laying granular activated carbon in the filter basins, the town, “because the cause could not be determined, stopped using its groundwater sources and shut down its treatment plant,” and now buys all its water from the Enterprise Bureau. Note that in the national table as of August 2025, Kin Town is still classified as “has its own water source.”
• Ishigaki City’s 28 in FY2024 was measured only in raw water (3–28 in FY2020–FY2025). There are 33 private water supplies (for a facility: in-house water systems for company housing, hospitals, bases and so on). None of the 14 that were tested exceeded 50 (FY2020 to August 2025).
• On health effects, the Ministry of the Environment’s “Frequently Asked Questions” introduces Okinawa Prefecture as an example in which the prefecture compared areas using existing health statistics and reportedly found no difference from the areas it compared. Japan has no standard for judging an individual’s health effects from blood levels. → How does PFAS affect the body?

Timeline

Rivers and groundwater (environmental monitoring)

These measure rivers or groundwater themselves, not tap water. The water is not necessarily used for drinking.

• The Dakujaku River (大工廻川), a tributary of the Hija River (a survey point that is not a water source), had a maximum of 266 ng/L in FY2025 and 233 in FY2026 (April–August) in the Enterprise Bureau’s measurements. Its maximum in FY2019 (Reiwa 1) was 1,675.
• In the Enterprise Bureau’s special surveys, 13 of 19 points around the Hija River intake pumping station, and 10 of 13 points upstream on the Tengan and Kawasaki rivers (December 2016–April 2017), exceeded the U.S. EPA lifetime health advisory (70 ng/L for PFOS and PFOA combined) that was being used as a reference at the time.
• In the Ministry of the Environment’s nationwide survey for FY2019 (Reiwa 1), the Kawasaki River (川崎川) in Okinawa City (Tengan River system, at Motokawa Bridge (元川橋)) had 475 ng/L, a spring in Ginowan City (Mendakari Hiigaa (メンダカリヒーガー)) had 815.3, and a spring in Nakagami District (中頭郡) (Shiriigaa (シリーガー)) had 1,188.0. These are river and spring values, not tap water values.
• The Okinawa Prefectural Department of Environmental Affairs (沖縄県環境部) carried out a prefecture-wide water quality survey of rivers and other waters in FY2016, and since FY2017 it has continued surveys of rivers, springs and other waters around U.S. military bases. The prefecture’s page says that “for Kadena Air Base and MCAS Futenma, based on the water quality survey results and groundwater flow surveys to date, it is highly likely that the main sources of contamination are within the two air bases” (“嘉手納飛行場及び普天間飛行場については、これまでの水質調査結果や地下水脈の調査結果から主な汚染源は両飛行場内である蓋然性が高く”), and that for well water around Camp Hansen, “there is a possibility that the source of contamination is within the base” (“汚染源は同基地内である可能性があります”).
• Between June 2016 and December 2021, the prefecture applied four times for on-site inspections of Kadena Air Base (嘉手納飛行場) (2 applications), MCAS Futenma (普天間飛行場) (1) and Camp Hansen (キャンプ・ハンセン) (1), and each time the U.S. side replied that permission was not granted. On-site inspections inside the bases to investigate the sources of contamination have not been allowed (excluding the joint surveys by the prefecture, the national government and the U.S. military after 2 spill accidents), so the prefecture’s view is based mainly on measurements outside the bases. In FY2024, the prefecture’s expert panel concluded for MCAS Futenma that “the likelihood has become even higher” (“蓋然性が更に高まった”).

Put it in terms of your own intake

Related explainers

• What happened in areas where high PFAS values were found in tap water? A timeline of Kibichuo, Tama, Okinawa and more
• How do you check PFAS in your local tap water? Reading the national tables and working out “what percent of the TDI”
• Do high PFAS values in rivers or groundwater mean high values in tap water? How guideline values differ from the tap water standard
• How does PFAS affect the body? Assessments by different bodies, and what a blood test can tell you
• Water filters and PFAS

Sources

• Okinawa Prefectural Enterprise Bureau: “Detection of organic fluorine compounds at the Enterprise Bureau”
• Okinawa Prefectural Enterprise Bureau: “Organic fluorine compounds (PFOS and PFOA)” (FAQ, efforts and background)
• Okinawa Prefectural Enterprise Bureau: Detection of organic fluorine compounds (FY2026 (Reiwa 8), updated September 25, 2026)
• Okinawa Prefectural Enterprise Bureau: Detection of organic fluorine compounds (past data)
• Okinawa Prefectural Enterprise Bureau: Intake status of the Chatan treatment plant (updated September 25, 2026)
• MLIT: “Examples of how water utilities and others have responded to PFOS and PFOA so far” (November 29, 2024)
• Ministry of the Environment and MLIT: List of results of the follow-up survey of PFOS and PFOA in water supplies (published December 25, 2025)
• Okinawa Prefectural Department of Environmental Affairs: “Organic fluorine compounds” (updated July 7, 2026)
• Ministry of the Environment: “Frequently Asked Questions” (PFAS)
• Ministry of the Environment: List of results of the FY2019 (Reiwa 1) nationwide survey of PFOS and PFOA levels (published June 11, 2020)

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.

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