PFAS in tap water: Oita Prefecture
In the national survey table, no water utility in Oita Prefecture exceeded 50 ng/L (PFOS and PFOA combined) in FY2020–FY2025. The highest value in the prefecture was 28 ng/L (FY2024, tap water) for the Kunisaki City water service (国東市水道事業), and the highest in FY2025 (through the end of August) was also in that city, at 26.
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 大分市上下水道局Water supply · 大分市 | — | nd | nd | nd | nd | nd | tap, plant outlet and raw |
| 由布市水道事業Water supply · 由布市 | — | nd | nd | nd | nd | nd | tap only |
| 別府市水道事業Water supply · 別府市 | nd | nd | nd | nd | nd | nd | tap and raw |
| 中津市上下水道事業Water supply · 中津市 | — | nd | nd | nd | nd | nd | tap, plant outlet and raw |
| 日田市水道事業Water supply · 日田市 | — | nd | nd | nd | nd | 6 | tap only |
| 佐伯市水道事業Water supply · 佐伯市 | — | nd | nd | nd | nd | nd | tap only |
| 臼杵市水道事業Water supply · 臼杵市 | — | nd | nd | nd | nd | nd | tap only |
| 津久見市水道事業Water supply · 津久見市 | — | nd | nd | nd | nd | nd | tap only |
| 竹田市上水道事業Water supply · 竹田市 | — | nd | nd | nd | nd | nd | tap only |
| 豊後高田市水道事業Water supply · 豊後高田市 | — | nd | nd | nd | nd | nd | tap only |
| 杵築市水道事業Water supply · 杵築市 | — | nd | nd | nd | 11 | 13 | tap only |
| 豊後大野市水道事業Water supply · 豊後大野市 | — | nd | nd | nd | 24 | 25 | tap only |
| 日出町水道事業Water supply · 日出町 | — | nd | nd | nd | nd | nd | tap only |
| 玖珠町水道事業Water supply · 玖珠町 | — | nd | nd | nd | nd | nd | tap only |
| 宇佐市水道事業Water supply · 宇佐市 | — | nd | nd | nd | nd | nd | tap only |
| 国東市水道事業Water supply · 国東市 | — | — | — | nd | 28 | 26 | tap only |
| 玖珠町水道用水供給事業Bulk supplier · 玖珠町Supplies: 綾垣簡易水道事業（玖珠町内の簡易水道区域） | — | nd | nd | nd | nd | nd | — |
| 上竹中簡易水道Small water supply | — | — | — | — | — | 5 | — |
| 下田口簡易水道Small water supply | — | — | — | — | — | nd | — |
| 高山簡易水道Small water supply | — | — | — | — | — | — | — |
| 武山簡易水道Small water supply | — | — | — | — | — | — | — |
| 乙見簡易水道Small water supply | — | — | — | — | — | planned | — |
| 保戸島・四浦東地区簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 平岩地区簡易水道Small water supply | — | — | — | — | — | — | — |
| 泉水簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 妙見瀨ノ口簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 下片ケ瀬簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 戸上簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 松本簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 倉木簡易水道Small water supply | — | — | — | — | — | nd | — |
| 菅生簡易水道Small water supply | — | — | — | — | — | nd | — |
| 城原簡易水道Small water supply | — | — | — | — | — | — | — |
| 荻簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 久住簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 都野簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 白丹簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 直入中央簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 川辺簡易水道事業Small water supply | — | — | — | — | nd | nd | — |
| 上自在簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 朝地簡易水道Small water supply | — | — | — | — | — | nd | — |
| 櫟木簡易水道Small water supply | — | — | — | — | — | nd | — |
| 朴木簡易水道Small water supply | — | — | — | — | — | — | — |
| 田代簡易水道Small water supply | — | — | — | — | — | planned | — |
| 櫛来簡易水道Small water supply | — | — | — | — | — | — | — |
| 来浦浜簡易水道Small water supply | — | — | — | — | — | — | — |
| 来浦中央簡易水道Small water supply | — | — | — | — | — | — | — |
| 姫島村簡易水道Small water supply · 姫島村 | — | — | — | nd | nd | nd | tap only |
| 統合簡易水道Small water supply | — | — | — | nd | nd | nd | tap only |
| 串野簡易水道Small water supply | — | — | — | — | nd | nd | — |
| 粟野簡易水道Small water supply | — | — | — | — | nd | — | — |
| 湯坪簡易水道Small water supply | — | — | — | — | nd | — | — |
| 日向下簡易水道Small water supply | — | — | — | — | — | nd | — |
| 宝泉寺簡易水道Small water supply | — | — | — | — | — | nd | — |
| 滝上簡易水道Small water supply | — | — | — | — | — | nd | — |
| 須久保簡易水道Small water supply | — | — | — | — | — | nd | — |
| 筋湯簡易水道Small water supply | — | — | — | — | — | nd | — |
| 綾垣簡易水道事業Small water supplybuys all its water — Buys from 玖珠町水道用水供給事業 | — | — | — | — | — | 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
- The values for the Oita City Waterworks and Sewerage Bureau (大分市上下水道局) were nd (below the detection or quantification limit) in every year from FY2021 to FY2025 (in the November 2024 table, its testing points were the tap, the treatment plant outlet and raw water).
- Kunisaki City (nd in FY2023 → 28 in FY2024 → 26 in FY2025), Bungo-ono City (豊後大野市) (nd → 24 → 25) and Kitsuki City (杵築市) (nd → 11 → 13) have had detectable values since FY2024. In the November 2024 table, all three cities are utilities whose testing point was “tap only” (the table does not list the testing points for values from October 2024 onward or for FY2025).
- Of the 57 rows in the national table, 10 have no testing records, and all of them are small water supply systems.
- There are 189 private water supplies (for a facility: in-house water systems for company housing, hospitals, schools and so on). None of the 49 that were tested exceeded 50 (FY2020 to August 2025).
Rivers and groundwater (environmental monitoring)
These measure rivers or groundwater themselves, not tap water. The water is not necessarily used for drinking.
- In the Ministry of the Environment’s nationwide survey for FY2019 (Reiwa 1), the Ototsu River (乙津川) in Oita City (at Beppo Bridge (別保橋)) had 142.6 ng/L of PFOS and PFOA combined (of which PFOA was 142.0), and groundwater in Oita City had 48.8 (of which PFOA was 48.0). These are river and groundwater measurements, not tap water values. Oita City’s tap water is nd, as noted above.
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)
- Ministry of the Environment: List of results of the FY2019 (Reiwa 1) nationwide survey of PFOS and PFOA levels (published June 11, 2020)
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.