PFAS in tap water: Shiga Prefecture
For tap water in Shiga Prefecture, the highest combined PFOS and PFOA value in FY2020–FY2025 (FY2025 through the end of August) was 30 ng/L (Ritto City (栗東市) in FY2022 and Moriyama City (守山市) in FY2023). No supplier exceeded 50 ng/L. The highest value was 20 in Moriyama in FY2024 and 19 ng/L, also in Moriyama, in FY2025.
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 彦根市水道事業Water supply · 彦根市 | — | nd | nd | nd | nd | nd | tap only |
| 湖南市上下水道事業所Water supply · 湖南市 | nd | nd | nd | nd | nd | — | plant outlet only |
| 野洲市上下水道事業所Water supply · 野洲市 | — | — | — | 15 | 14 | — | tap and raw |
| 大津市水道事業Water supply · 大津市 | 5 | 6 | 6 | 7 | 6 | nd | tap and raw |
| 草津市水道事業Water supply · 草津市 | — | 12 | nd | 7 | nd | nd | plant outlet and raw |
| 甲賀市水道事業Water supply · 甲賀市 | — | — | — | 11 | 10 | 11 | tap and raw |
| 栗東市上下水道事業所Water supply · 栗東市 | — | 13 | 30 | 23 | 17 | — | tap, plant outlet and raw |
| 守山市Water supply · 守山市 | 23 | 23 | 24 | 30 | 20 | 19 | tap, plant outlet and raw |
| 長浜水道企業団Water supply · 長浜市 | — | — | 5 | 5 | nd | nd | plant outlet only |
| 高島市水道事業Water supply · 高島市 | — | — | — | — | nd | nd | raw water only |
| 米原市水道事業Water supply · 米原市 | — | — | — | — | nd | nd | tap only |
| 日野町水道事業Water supply · 日野町 | — | — | — | — | nd | — | tap and plant outlet |
| 豊郷町水道事業Water supply · 豊郷町 | — | — | nd | nd | nd | nd | tap only |
| 甲良町水道事業Water supply · 甲良町 | — | — | nd | nd | nd | nd | — |
| 多賀町水道事業Water supply · 多賀町 | — | — | — | — | nd | nd | raw water only |
| 長浜水道企業団 浅井上水道事業Water supply · 長浜市 | — | — | — | nd | nd | nd | plant outlet only |
| 長浜水道企業団 高月浄水場事業Water supply · 長浜市 | — | — | — | nd | nd | nd | plant outlet only |
| 愛知郡広域行政組合Water supply | — | — | — | — | nd | — | — |
| 東近江市水道事業Water supply · 東近江市 | — | — | — | nd | 6 | nd | tap and plant outlet |
| 近江八幡水道事業Water supply · 近江八幡市 | 8 | 7 | 6 | 19 | 13 | 7 | tap only |
| 竜王町水道事業Water supply · 竜王町buys all its water — Buys from 湖南水道用水供給事業 | — | — | — | — | 7 | 5 | tap only |
| 湖南水道用水供給事業Bulk supplier · 湖南市Supplies: 近江八幡市、草津市、守山市、栗東市、甲賀市、野洲市、湖南市、東近江市、日野町、竜王町 | 6 | 7 | 8 | 7 | 8 | 6 | plant outlet and raw |
| 米原市 伊吹北部簡易水道Small water supply · 米原市 | — | — | — | — | nd | nd | — |
| 米原市 甲津原簡易水道Small water supply · 米原市 | — | — | — | — | nd | nd | — |
| 長浜水道企業団 湖北西部地区簡易水道事業Small water supply · 長浜市 | — | — | — | nd | nd | nd | plant outlet only |
| 長浜水道企業団 湖北中部地区簡易水道事業Small water supply · 長浜市 | — | — | — | nd | nd | nd | plant outlet only |
| 長浜水道企業団 木之本簡易水道事業Small water supply · 長浜市 · 2 systems | — | — | — | nd | nd | nd | plant outlet only |
| 長浜水道企業団 西浅井簡易水道事業Small water supply · 長浜市 · 4 systems | — | — | — | nd | nd | nd | plant outlet only |
| 長浜水道企業団 余呉・木之本簡易水道事業Small water supply · 長浜市 · 5 systems | — | — | — | nd | nd | nd | — |
| 長浜水道企業団 郡上地区簡易水道Small water supply · 長浜市 | — | — | — | nd | nd | nd | plant outlet only |
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 the table published in 2024, the testing points for Ritto and Moriyama mix three types: the tap, the treatment plant outlet and raw water (before treatment). The national table does not show which point gave the maximum value.
- The prefecture’s Konan bulk water supply (湖南水道用水供給事業, which sells water to municipalities) reported 6–8 ng/L, and Otsu City Waterworks (大津市水道事業) reported nd–7 ng/L.
- Among private water supplies (for a facility, such as company housing or hospitals), none of the 30 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.