PFAS in tap water: Kagawa Prefecture
In the national survey table, Kagawa Prefecture has only two rows: the Kagawa Prefecture Wide-Area Water Supply Authority (香川県広域水道企業団水道事業) and the Naoshima Town small water supply system (直島町簡易水道事業). Neither exceeded 50 ng/L (PFOS and PFOA combined) in FY2020–FY2025. The highest value in the prefecture was 36 ng/L for the authority (FY2025, through the end of August); in FY2024 it was 26.
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 香川県広域水道企業団水道事業Water supply | — | — | 23 | 14 | 26 | 36 | tap, plant outlet and raw |
| 直島町簡易水道事業Small water supply · 直島町 | — | — | — | — | 6 | nd | tap and raw |
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
- The authority’s values were 23 in FY2022, 14 in FY2023, 26 in FY2024 and 36 in FY2025. In the November 2024 table, its testing points were a mix of tap, treatment plant outlet and raw water (water before treatment), and the table does not say which point each value comes from. Because the value is the highest one in that fiscal year within a single utility, it is not necessarily the value at your own tap.
- When the table was published in November 2024, the authority’s FY2024 value was 9 (through the end of September), but in the December 2025 table it is 26. The national table does not give a reason.
- The Naoshima Town small water supply system was 6 in FY2024 and nd (below the detection or quantification limit) in FY2025. There are 33 private water supplies (for a facility: in-house water systems for company housing, hospitals and so on). None of the 29 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.