PFAS in tap water: Nara Prefecture
For tap water in Nara Prefecture, the highest combined PFOS and PFOA value in FY2020–FY2025 (FY2025 through the end of August) was 46 ng/L at the Yamazoe Village small water supply system (山添村簡易水道事業) in FY2023. This was measured only in raw water (before treatment), and later values were 13 and 10. No supplier exceeded 50 ng/L. The highest value was 27 at the Nara Prefecture Regional Water Supply Authority’s Ikoma office (奈良県広域水道企業団 生駒事務所) in FY2024, and 21 ng/L at the same authority’s Tenri office (天理事務所) and the Soni Village small water supply system (曽爾村簡易水道事業) in FY2025.
Levels by utility (PFOS + PFOA combined, ng/L)
| Utility | FY2020 | FY2021 | FY2022 | FY2023 | FY2024 | FY2025* | Sampled at |
|---|---|---|---|---|---|---|---|
| 奈良県広域水道企業団橿原事務所Water supply · 橿原市buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団生駒事務所Water supply · 生駒市 | 12 | 31 | 23 | 22 | 27 | 17 | — |
| 奈良県広域水道企業団桜井事務所Water supply · 桜井市 | — | nd | nd | nd | 7 | 4 | — |
| 奈良県広域水道企業団香芝事務所Water supply · 香芝市buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | nd | nd | — |
| 奈良県広域水道企業団天理事務所Water supply · 天理市 | — | — | 16 | 16 | 15 | 21 | — |
| 奈良県広域水道企業団大和高田事務所Water supply · 大和高田市buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団御所事務所Water supply · 御所市 | — | nd | 6 | nd | nd | nd | — |
| 葛城市上下水道事業Water supply · 葛城市Also buys from: 奈良県広域水道企業団水道用水供給事業 | — | — | — | nd | 19 | 10 | raw water only |
| 奈良県広域水道企業団宇陀事務所Water supply · 宇陀市 | — | — | — | — | 9 | 7 | — |
| 奈良県広域水道企業団平群事務所Water supply · 平群町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | 3 | — |
| 奈良県広域水道企業団三郷事務所Water supply · 三郷町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | 3 | — |
| 奈良県広域水道企業団斑鳩事務所Water supply · 斑鳩町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | 4 | — |
| 奈良県広域水道企業団安堵事務所Water supply · 安堵町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団磯城事務所（田原本町）Water supply · 田原本町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | 4 | — |
| 奈良県広域水道企業団磯城事務所（三宅町）Water supply · 三宅町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団磯城事務所（川西町）Water supply · 川西町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団高取事務所Water supply · 高取町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | nd | nd | — |
| 奈良県広域水道企業団明日香事務所Water supply · 明日香村buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団王寺事務所Water supply · 王寺町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | nd | nd | — |
| 奈良県広域水道企業団広陵事務所Water supply · 広陵町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | nd | nd | nd | — |
| 奈良県広域水道企業団河合事務所Water supply · 河合町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | nd | — | nd | — | nd | — |
| 奈良県広域水道企業団吉野事務所Water supply · 吉野町 | — | — | — | — | nd | nd | — |
| 奈良県広域水道企業団大淀事務所Water supply · 大淀町 | nd | nd | nd | nd | nd | nd | — |
| 奈良県広域水道企業団下市事務所Water supply · 下市町 | — | — | — | — | — | nd | — |
| 奈良県広域水道企業団大和郡山事務所Water supply · 大和郡山市 | 6 | 8 | 12 | 9 | 10 | 5 | — |
| 奈良県広域水道企業団五條事務所Water supply · 五條市 | — | — | — | — | nd | nd | — |
| 奈良県広域水道企業団上牧事務所Water supply · 上牧町buys all its water — Buys from 奈良県広域水道企業団水道用水供給事業 | — | — | — | — | nd | nd | — |
| 奈良市水道事業Water supply · 奈良市Also buys from: 奈良県広域水道企業団水道用水供給事業 | — | 15 | 34 | 9 | 12 | 15 | plant outlet and raw |
| 都祁水道事業Water supply | — | 8 | 11 | 9 | 8 | 12 | plant outlet and raw |
| 奈良県広域水道企業団水道用水供給事業Bulk supplierSupplies: 奈良市、葛城市 | 6 | 5 | 5 | 5 | 4 | 4 | — |
| 月ヶ瀬簡易水道事業Small water supply | — | 13 | 16 | 17 | 14 | 13 | tap and raw |
| 山添村簡易水道事業Small water supply · 山添村 | — | — | — | 46 | 13 | 10 | raw water only |
| 曽爾村簡易水道事業Small water supply · 曽爾村 | — | — | — | — | — | 21 | — |
| 御杖村簡易水道事業Small water supply · 御杖村 | — | — | — | — | — | nd | — |
| 黒滝村簡易水道事業Small water supply · 黒滝村 | — | — | — | — | nd | nd | — |
| 天川村簡易水道事業Small water supply · 天川村 | — | — | — | — | 5 | — | — |
| 野迫川村簡易水道事業Small water supply · 野迫川村 | — | — | — | — | — | nd | — |
| 十津川村簡易水道事業Small water supply · 十津川村 | — | — | — | — | nd | nd | tap only |
| 下北山村Small water supply · 下北山村 | — | — | — | — | nd | — | — |
| 上北山村簡易水道事業Small water supply · 上北山村 | — | — | — | — | — | nd | — |
| 川上村簡易水道事業Small water supply · 川上村 | — | — | — | — | 5 | — | — |
| 東吉野村簡易水道Small water supply · 東吉野村 | — | — | — | — | — | 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
- Of the 42 rows for the prefecture, 16 are suppliers that buy all their water from another supplier (they have no water source of their own). The Nara Prefecture Regional Water Supply Authority’s bulk supply was 4–6 ng/L. For these suppliers, look at the values of the supplier they buy from as well. → How to check
- Nara City Waterworks (奈良市水道事業) reported 9–34 ng/L (highest in FY2022), with testing points at the treatment plant outlet and raw water.
- Among private water supplies (for a facility, such as company housing or hospitals), 1 of the 31 operators tested in the prefecture exceeded the provisional target value (50 ng/L). The facility is not named in the national documents.
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.