PFAS in tap water: Nagasaki Prefecture
In the national survey table, no water utility in Nagasaki Prefecture exceeded 50 ng/L (PFOS and PFOA combined) in FY2020–FY2025. The highest value in the prefecture was 48 ng/L (FY2024) for the Shinkamigoto Town water service (新上五島町水道事業), and the highest in FY2025 (through the end of August) was 47 in Minamishimabara City (南島原市). Shinkamigoto Town’s 48 was measured only in raw water (water before treatment). In the November 2024 table, Minamishimabara City’s testing point was “raw water only” (the table does not list the testing point for its FY2025 value). Among utilities whose testing includes the tap, the highest was 42 in Togitsu Town (時津町) (FY2021).
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 長崎市水道事業Water supply · 長崎市 | — | — | — | 6 | 7 | nd | tap and raw |
| 佐世保市水道局Water supply · 佐世保市 | — | — | nd | 4 | nd | nd | tap, plant outlet and raw |
| 平戸市水道事業Water supply · 平戸市 | — | — | — | — | nd | nd | tap and raw |
| 大村市水道事業Water supply · 大村市 | — | nd | nd | 28 | 10 | 9 | tap, plant outlet and raw |
| 諫早市上下水道事業Water supply · 諫早市 | 11 | 12 | 12 | 13 | 30 | 14 | tap and raw |
| 松浦市水道事業Water supply · 松浦市 | — | — | — | — | nd | nd | tap only |
| 佐々町水道事業Water supply · 佐々町 | — | — | — | — | 5 | nd | tap and raw |
| 川棚町水道事業Water supply · 川棚町 | — | — | — | — | nd | nd | raw water only |
| 島原市水道事業Water supply · 島原市 | nd | nd | nd | nd | nd | 8 | tap only |
| 長与町水道事業Water supply · 長与町 | — | — | — | nd | nd | nd | tap and raw |
| 時津町上水道事業Water supply · 時津町 | — | 42 | 39 | 34 | 8 | 14 | tap and plant outlet |
| 壱岐市水道事業Water supply · 壱岐市 | — | — | — | — | 23 | 18 | raw water only |
| 波佐見町上水道事業Water supply · 波佐見町 | — | — | — | — | nd | nd | tap and raw |
| 南島原市水道事業Water supply · 南島原市 | — | — | — | — | 13 | 47 | raw water only |
| 西海市水道事業Water supply · 西海市 | — | — | — | — | nd | — | raw water only |
| 東彼杵町水道事業Water supply · 東彼杵町 | — | — | — | — | nd | 10 | raw water only |
| 五島市水道事業Water supply · 五島市 | — | — | — | — | nd | nd | — |
| 対馬市水道事業Water supply · 対馬市 | — | — | — | — | 1.2 | — | — |
| 新上五島町水道事業Water supply · 新上五島町 | — | — | — | nd | 48 | nd | raw water only |
| 雲仙市水道事業Water supply · 雲仙市 | — | — | — | — | 22 | 14 | tap only |
| 奈留地区簡易水道事業Small water supply | — | — | — | — | nd | nd | — |
| 久賀地区簡易水道事業Small water supply | — | — | — | — | nd | nd | — |
| 椛島簡易水道事業Small water supply | — | — | — | — | nd | nd | — |
| 宮簡易水道組合Small water supply | — | — | — | — | nd | nd | raw water only |
| 佐世保市黒島本村簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | — | tap only |
| 佐世保市田代簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | nd | tap only |
| 佐世保市赤木簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | nd | tap only |
| 佐世保市上木場簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | — | tap only |
| 佐世保市平松簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | — | tap only |
| 佐世保市下宇戸・川谷地区簡易水道事業Small water supply · 佐世保市 | — | — | — | nd | — | — | tap only |
| 佐世保市世知原地区簡易水道事業Small water supply · 佐世保市 | — | — | — | nd | — | — | tap only |
| 佐世保市上野原簡易水道事業Small water supply · 佐世保市 | — | — | — | nd | — | — | tap only |
| 佐世保市神浦地区簡易水道事業Small water supply · 佐世保市 | — | — | — | nd | — | — | tap only |
| 佐世保市北部簡易水道事業(宇久)Small water supply · 佐世保市 | — | — | — | nd | — | — | tap only |
| 佐世保市平地区簡易水道事業Small water supply · 佐世保市 | — | — | — | nd | — | — | tap only |
| 佐世保市矢岳地区簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | — | tap only |
| 佐世保市船ノ村地区簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | nd | tap only |
| 佐世保市北部地区簡易水道事業(鹿町）Small water supply · 佐世保市 | — | — | — | nd | nd | nd | tap and raw |
| 佐世保市歌ヶ浦地区簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | nd | tap only |
| 佐世保市神林地区簡易水道事業Small water supply · 佐世保市 | — | — | — | — | nd | nd | tap only |
| 西海市簡易水道事業（崎戸町江島）Small water supply · 西海市 | — | — | — | — | nd | — | raw water only |
| 西海市簡易水道事業（崎戸町平島）Small water supply · 西海市 | — | — | — | — | nd | — | raw water only |
| 西海市簡易水道事業（大瀬戸町松島地区）Small water supply · 西海市 | — | — | — | — | nd | — | raw water only |
| 小値賀町簡易水道事業Small water supply · 小値賀町 | — | — | — | — | nd | nd | tap only |
| 里美営農飲雑用水利用組合Small water supply | — | — | — | — | — | nd | — |
| 諫早市 赤崎Small water supply · 諫早市 | — | — | — | — | — | nd | — |
| 諫早市 黒崎Small water supply · 諫早市 | — | — | — | — | — | nd | — |
| 諫早市 小野島Small water supply · 諫早市 | — | — | — | — | nd | — | — |
| 諫早市 川内町Small water supply · 諫早市 | — | — | — | — | — | nd | — |
| 諫早市 長野Small water supply · 諫早市 | — | — | — | — | — | nd | — |
| 諫早市 川内町新地Small water supply · 諫早市 | — | — | — | — | — | nd | — |
| 諫早市 浜浦Small water supply · 諫早市 | — | — | — | — | nd | — | — |
| 諫早市 柳谷Small water supply · 諫早市 | — | — | — | — | — | 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
- Raw water is not covered by the tap water standard. Shinkamigoto Town was nd in FY2023, 48 in FY2024 and nd in FY2025. Minamishimabara City was 13 in FY2024 and 47 in FY2025; when the table was published in November 2024, its FY2024 value was 5 (through the end of September).
- Togitsu Town: 42→39→34→8→14 (FY2021→FY2025; in the November 2024 table, its testing points were the tap and the treatment plant outlet). Isahaya City (諫早市) had 30 in FY2024, and Omura City (大村市) had 28 in FY2023.
- All 53 rows in the prefecture have testing records, and no service buys all its water. There are 144 private water supplies (for a facility: in-house water systems for company housing, hospitals and so on). None of the 80 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.