PFAS in tap water: Yamaguchi Prefecture
In the national survey table, no water utility in Yamaguchi Prefecture exceeded 50 ng/L (PFOS and PFOA combined) in FY2020–FY2025. The highest value in the prefecture was 32 ng/L (FY2020, measured at the tap and the treatment plant outlet) for the Hofu City water service (防府市水道事業). The highest value in the prefecture was 12 in FY2024 and 8 in FY2025 (through the end of August), both in Hofu City.
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 美祢市水道事業Water supply · 美祢市 | — | — | — | nd | nd | — | tap only |
| 周防大島町水道事業Water supply · 周防大島町Also buys from: 柳井地域広域水道企業団 | — | — | — | nd | nd | nd | raw water only |
| 宇部市水道局Water supply · 宇部市 | nd | nd | nd | nd | nd | — | plant outlet and raw |
| 岩国市水道局Water supply · 岩国市Also buys from: 柳井地域広域水道企業団 | nd | — | 9 | nd | nd | nd | tap and raw |
| 山陽小野田市水道事業Water supply · 山陽小野田市 | nd | nd | nd | nd | nd | — | plant outlet and raw |
| 光市水道局Water supply · 光市 | nd | nd | nd | nd | nd | — | tap and raw |
| 防府市水道事業Water supply · 防府市 | 32 | 25 | 19 | 15 | 12 | 8 | tap and plant outlet |
| 長門市上水道事業Water supply · 長門市 | — | — | — | nd | nd | nd | tap only |
| 田布施・平生水道事業Water supply · 平生町Also buys from: 柳井地域広域水道企業団 | — | — | — | — | nd | 3 | — |
| 萩市上下水道局Water supply · 萩市 | — | nd | nd | nd | nd | 3 | tap only |
| 柳井市水道事業Water supply · 柳井市buys all its water — Buys from 柳井地域広域水道企業団 | — | — | — | — | — | — | — |
| 山口市水道事業Water supply · 山口市 | — | — | 10 | 5 | 9 | nd | tap and raw |
| 下関市水道事業Water supply · 下関市 | nd | nd | 5 | nd | nd | nd | tap and raw |
| 周南市水道事業Water supply · 周南市 | nd | nd | nd | nd | nd | — | tap and raw |
| 下松市水道事業Water supply · 下松市 | nd | nd | nd | nd | nd | — | tap and raw |
| 柳井地域広域水道企業団Bulk supplier · 柳井市Supplies: 柳井市、周防大島町、上関町、田布施町、平生町、岩国市 | nd | nd | nd | nd | nd | nd | plant outlet and raw |
| 阿武町簡易水道事業Small water supply · 阿武町 | — | — | — | — | nd | — | — |
| 米川簡易水道事業Small water supply | nd | nd | nd | nd | nd | — | tap and raw |
| 俵山簡易水道事業Small water supply | — | — | — | nd | nd | — | tap only |
| 山口市阿東簡易水道事業Small water supply · 山口市 | — | — | 10 | 12 | 6 | nd | — |
| 岩国市簡易水道事業Small water supply · 岩国市 | — | — | — | nd | nd | — | tap only |
| 柳井市平郡簡易水道事業Small water supply · 柳井市 | — | — | — | 8 | 5 | 8 | tap only |
| 和木町簡易水道事業Small water supply · 和木町 | — | — | — | — | — | nd | — |
| 上関統合簡易水道事業Small water supplybuys all its water — Buys from 柳井地域広域水道企業団 | — | — | — | — | — | — | — |
| 上関町祝島・八島統合簡易水道事業Small water supply · 上関町 | — | — | — | — | nd | nd | — |
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
- Hofu City’s values fell every year: 32→25→19→15→12→8 (FY2020→FY2025). Each value in the national table is the single highest value in that fiscal year.
- Apart from Hofu City, the highest values were 12 for the Yamaguchi City Ato small water supply system (山口市阿東簡易水道), 10 for the Yamaguchi City water service (山口市水道事業) and 9 for Iwakuni City (岩国市). Shimonoseki City (下関市) was nd (below the detection or quantification limit) to 5.
- There are 63 private water supplies (for a facility: in-house water systems for company housing, hospitals, bases and so on). None of the 24 that were tested exceeded 50 (FY2020 to August 2025).
Put it in terms of your own intake
- Intake from water
- — ng/kg/day
- Compared with Japan’s tolerable daily intake (PFOS and PFOA, 20 ng/kg bw/day each)
- —
- Compared with EFSA’s tolerable weekly intake (4 PFAS combined, 4.4 ng/kg bw/week ≈ 0.63 a day)
- —
- Compared with intake from 37 foods (MAFF estimate: PFOS 0.13 + PFOA 0.09 = 0.22 ng/kg bw/day; the 37 foods make up about half of what people eat by amount)
- —
The combined value is treated as a single substance (in reality it is split between PFOS and PFOA, so the share of Japan’s TDI would be smaller). EFSA’s value is for the sum of PFOA, PFNA, PFHxS and PFOS; tap-water values here do not include PFNA or PFHxS. This calculation shows how the same intake reads differently against different yardsticks; it does not judge health effects.
Related explainers
Sources
- 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)
- Ministry of the Environment and MLIT: Results of the follow-up survey (December 25, 2025)
- Ministry of the Environment and MLIT: List of survey results (published November 29, 2024)
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.