PFAS in tap water: Shimane Prefecture
For tap water in Shimane Prefecture, the highest combined PFOS and PFOA value in FY2020–FY2025 (FY2025 through the end of August) was 20 ng/L at Unnan City Waterworks (雲南市水道事業) in FY2025. No supplier exceeded 50 ng/L. The highest value in FY2024 was 7 ng/L in Masuda City (益田市).
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 安来市水道事業Water supply · 安来市Also buys from: 島根県水道用水供給事業 | — | — | — | nd | nd | — | — |
| 奥出雲町水道事業Water supply · 奥出雲町 | — | — | — | — | — | nd | — |
| 斐川宍道水道企業団Water supply | — | — | nd | — | — | nd | plant outlet only |
| 浜田市水道事業Water supply · 浜田市 | — | — | — | — | nd | nd | tap only |
| 江津市水道事業Water supply · 江津市Also buys from: 江の川水道用水供給事業 | — | — | — | nd | — | nd | raw water only |
| 益田市水道事業Water supply · 益田市 | — | 13 | 11 | 16 | 7 | 18 | plant outlet only |
| 吉賀町水道事業Water supply · 吉賀町 | — | — | — | — | — | nd | — |
| 隠岐の島町水道事業Water supply · 隠岐の島町 | — | — | — | — | nd | — | — |
| 出雲市水道事業Water supply · 出雲市Also buys from: 島根県水道用水供給事業 | — | — | — | nd | nd | nd | plant outlet only |
| 雲南市水道事業Water supply · 雲南市Also buys from: 島根県水道用水供給事業 | — | — | — | — | nd | 20 | plant outlet only |
| 大田市水道事業Water supply · 大田市Also buys from: 江の川水道用水供給事業 | — | — | — | — | nd | nd | raw water only |
| 邑南町水道事業Water supply · 邑南町 | — | — | — | — | nd | nd | — |
| 津和野町水道事業Water supply · 津和野町 | — | — | — | — | nd | nd | raw water only |
| 松江市水道事業Water supply · 松江市Also buys from: 島根県水道用水供給事業 | nd | nd | nd | nd | nd | nd | — |
| 島根県水道用水供給事業Bulk supplierSupplies: 松江市、出雲市、安来市、雲南市 | nd | nd | nd | nd | nd | nd | plant outlet only |
| 江の川水道用水供給事業Bulk supplierSupplies: 江津市、大田市 | nd | nd | nd | nd | nd | nd | plant outlet only |
| 川本町簡易水道事業Small water supply · 川本町 | — | — | — | — | — | nd | — |
| 美郷町簡易水道事業Small water supply · 美郷町 | — | — | — | — | — | nd | — |
| 海士町簡易水道Small water supply · 海士町 | — | — | — | — | nd | — | raw water only |
| 西ノ島町簡易水道事業Small water supply · 西ノ島町 | — | — | — | — | nd | — | — |
| 波根給水組合Small water supply | — | — | — | — | — | planned | — |
| 東中津簡易水道給水組合Small water supply | — | — | — | — | — | 4 | — |
| 飯南町簡易水道事業Small water supply · 飯南町 | — | — | — | — | nd | nd | raw water only |
| 知夫村簡易水道事業Small water supply · 知夫村 | — | — | — | — | — | 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
- Unnan City Waterworks was nd (below the quantification limit) in FY2024 and 20 ng/L in FY2025; in the table published in 2024, its testing point is the treatment plant outlet. Masuda City Waterworks reported 7–18 ng/L (treatment plant outlet).
- Matsue City Waterworks (松江市水道事業) and the prefecture’s two bulk water suppliers (which sell water to municipalities), Shimane Prefecture (島根県) and Gonokawa (江の川), were nd in every year from FY2020 to FY2025.
- Among private water supplies (for a facility, such as company housing or hospitals), none of the 15 tested in the prefecture was found to exceed the provisional target value (50 ng/L) (through the end of 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, “Survey on PFOS and PFOA in Water Supply,” follow-up survey: list of results (published December 25, 2025)
- Ministry of the Environment and MLIT, list of results (published November 29, 2024; testing point column)
- Same follow-up survey, attachment (status of private water supplies by prefecture)
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.