PFAS in tap water: Kochi Prefecture
In the national survey table, no water utility in Kochi Prefecture exceeded 50 ng/L (PFOS and PFOA combined) in FY2020–FY2025. The highest value in the prefecture was 26 ng/L (FY2025, through the end of August) for the Kuroshio Town water service (黒潮町水道事業). The highest value in the prefecture in FY2024 was 14 in Shimanto City (四万十市) (measured only in raw water, meaning water before treatment).
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 室戸市水道事業Water supply · 室戸市 | — | — | — | — | 2 | nd | raw water only |
| 安芸市水道事業Water supply · 安芸市 | — | — | 0.8 | 1.4 | 1 | nd | raw water only |
| 南国市上水道事業Water supply · 南国市 | 5 | 9.96 | 2.43 | 3.35 | 7.49 | 15 | tap only |
| 高知市水道事業Water supply · 高知市 | — | nd | 15 | 7 | 13 | nd | tap, plant outlet and raw |
| 土佐市水道事業Water supply · 土佐市 | — | — | — | — | nd | nd | raw water only |
| 須崎市水道事業Water supply · 須崎市 | — | 7 | 8 | 8 | 6 | — | raw water only |
| 宿毛市水道事業Water supply · 宿毛市 | — | — | — | — | nd | nd | raw water only |
| 土佐清水市水道事業Water supply · 土佐清水市 | — | — | — | — | nd | nd | raw water only |
| 四万十市水道事業Water supply · 四万十市 | — | — | — | — | 14 | 23.38 | raw water only |
| 香南市水道事業Water supply · 香南市 | — | — | — | — | 8 | — | — |
| 香美市水道事業Water supply · 香美市 | — | — | — | — | 2 | nd | raw water only |
| いの町水道事業Water supply · いの町 | — | — | — | — | nd | nd | tap only |
| 佐川町水道事業Water supply · 佐川町 | — | — | — | — | 1 | nd | raw water only |
| 四万十町水道事業Water supply · 四万十町 | — | — | — | — | — | nd | — |
| 黒潮町水道事業Water supply · 黒潮町 | — | — | — | — | 12 | 26 | — |
| 宿毛市鵜来島簡易水道事業Small water supply · 宿毛市 | — | — | — | — | nd | nd | raw water only |
| 宿毛市沖の島簡易水道事業Small water supply · 宿毛市 | — | — | — | — | nd | nd | raw water only |
| 香美市簡易水道事業Small water supply · 香美市 · 3 systems | — | — | — | — | — | nd | — |
| 東洋町簡易水道事業Small water supply · 東洋町 | — | — | — | — | — | nd | — |
| 奈半利町簡易水道事業Small water supply · 奈半利町 | — | — | — | — | — | nd | — |
| 田野町簡易水道Small water supply · 田野町 | — | — | — | — | nd | nd | tap only |
| 安田町簡易水道事業Small water supply · 安田町 | — | — | — | — | — | nd | — |
| 馬路村簡易水道Small water supply · 馬路村 | — | — | — | — | — | nd | — |
| 芸西村簡易水道Small water supply · 芸西村 | — | — | — | — | 1.1 | — | — |
| 本山町簡易水道事業Small water supply · 本山町 | — | — | — | — | nd | nd | raw water only |
| 大豊町簡易水道事業Small water supply · 大豊町 | — | — | — | — | nd | — | — |
| 土佐町簡易水道事業Small water supply · 土佐町 | — | — | — | — | nd | — | raw water only |
| 仁淀川町簡易水道事業Small water supply · 仁淀川町 | — | — | — | — | — | nd | — |
| 中土佐地区簡易水道事業Small water supply · 中土佐町 | — | — | — | — | — | nd | — |
| 大野見地区簡易水道事業Small water supply | — | — | — | — | — | nd | — |
| 越知町簡易水道事業Small water supply · 越知町 | — | — | — | — | nd | — | raw water only |
| 梼原町簡易水道事業Small water supply · 梼原町 | — | — | — | — | nd | nd | — |
| 日高村Small water supply · 日高村 | — | — | — | — | nd | nd | tap only |
| 津野町簡易水道事業Small water supply · 津野町 | — | — | — | — | — | nd | — |
| 大月町Small water supply · 大月町 | — | — | — | — | nd | nd | raw water only |
| 三原村簡易水道事業Small water supply · 三原村 | — | — | — | — | — | nd | — |
| 北川村Small water supply · 北川村 | — | — | — | — | nd | — | raw water 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 November 2024 table, Shimanto City is a utility whose testing point was “raw water only” (the table does not list the testing point for its FY2025 value of 23.38). Susaki City (須崎市), Muroto City (室戸市) and Kami City (香美市) were also “raw water only” in the November 2024 table. A raw water value is not necessarily the value of the water delivered to homes. Kuroshio Town had no testing record in the November 2024 table, and a value first appeared in the December 2025 table. The table does not list the testing point.
- Kochi City (高知市) was nd (below the detection or quantification limit) to 15 in FY2021–FY2025, and Nankoku City (南国市) was 2.43–15 (in the November 2024 table, Nankoku City’s testing point was “tap only”). In FY2025, Nankoku City was 15 and Kochi City was nd.
- There are 35 private water supplies (for a facility: in-house water systems for company housing, hospitals and so on). None of the 11 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; testing point column)
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.