PFAS in tap water: Tochigi 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

Good to know

• In February 2025, Shimotsuke City found values above the provisional target value in the tap water of the Ishibashi No. 2 distribution reservoir (石橋第2配水場) (serving parts of Kamikoyama (上古山) and Shimokoyama (下古山)), and took measures such as setting up temporary water distribution points (announced by Tochigi Prefecture). The FY2025 value in the national table (63) covers through the end of August.
• In the national release of December 2025, of the 19 utilities nationwide that exceeded the provisional target value between FY2020 and the end of August 2025, 18 had taken measures, and the remaining one was described as “emergency measures are in place, and measures are scheduled to be implemented within this fiscal year,” but which utility it is was not stated.
• Besides Shimotsuke City, the only utility above 25 ng/L was Moka City (真岡市), at 48 (FY2021) and 26 (FY2025). Moka City measures only in raw water (water before treatment at the plant).
• Tochigi City (栃木市) was 7–23 (treatment plant outlet), Kaminokawa Town (上三川町) 10–21 (tap), and Utsunomiya City (宇都宮市) nd–12. The bulk water suppliers Kitanasu (北那須) and Kinu (鬼怒) were nd in every year they measured (FY2021–FY2025).
• The prefecture publishes a list of links to the PFOS and PFOA test result pages of its cities, towns and the prefectural Public Enterprise Bureau. You can check the latest values for your city or town there. → How do I look up PFAS in my local tap water?
• Private water supplies (for a facility) were tested at 141 of the 318 operators, and 4 exceedances have been confirmed (none national-government, through the end of August 2025).

Timeline

Rivers and groundwater (environmental monitoring)

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

• In November and December 2024, Utsunomiya City announced that PFOS and PFOA in wells in the city exceeded the groundwater guideline value (50 ng/L). In response, the prefecture and Shimotsuke City have been surveying groundwater in Shimotsuke City (Tochigi Prefecture).
• In the groundwater survey by the prefecture and Shimotsuke City, a well in Shimokoyama was found above the guideline value in January 2025, and in the second survey, 1 of 10 wells in Kamikoyama and Shimokoyama measured 59 ng/L. Well users have been informed about testing and other matters.
• On February 28, 2025, the prefecture announced that it had received information from the Japan Ground Self-Defense Force (JGSDF) Camp Utsunomiya (陸上自衛隊宇都宮駐屯地) that 112 ng/L had been detected in one well on the camp. The prefecture’s documents do not mention the cause.
• These are measurements of well water (groundwater), compared with the “guideline value,” which is separate from the water supply standard. → High levels in rivers or groundwater = high levels in tap water?

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
• Japan’s PFAS standard for tap water, “50 ng/L”: how was it set, and how does it differ from the U.S. and EU?
• Water filters and PFAS

Sources

• Tochigi Prefecture, “Groundwater in Shimokoyama, Shimotsuke City exceeding the provisional guideline value for PFOS and PFOA (2nd report)” (updated March 6, 2025)
• Tochigi Prefecture, “Water quality test results for PFOS and PFOA in water supplies” (links to cities, towns and others)
• Ministry of the Environment and MLIT, “Results of the follow-up survey on PFOS and PFOA in water supplies” (December 25, 2025)
• Same, list of survey results (updated), Excel (annual maximums, FY2020–FY2025)
• Ministry of the Environment and MLIT, list of survey results, Excel (published November 29, 2024)
• Same, follow-up survey annex (status of private water supplies by prefecture)
• Ministry of the Environment, notice on the enforcement of the partial revision of the Ministerial Ordinance on Water Quality Standards, etc. (No. 2506301, June 30, 2025)

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.

Other prefectures

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