PFAS in tap water: Okayama Prefecture

Levels by utility (PFOS + PFOA combined, ng/L)

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 are for water from Kibichuo’s Enjo treatment plant (円城浄水場), which draws from the Kobira Dam (河平ダム) and serves 522 households, about 1,000 people. The test results in the town’s documents are 800 in November 2020, 1,200 in October 2021 and 1,400 ng/L in October 2022. While the town was cooperating with the Japan Water Works Association’s “FY2022 Waterworks Statistics Survey,” the public health center contacted the town about the 1,400 ng/L on October 13, 2023, and the town made it public on October 17 (town documents). At the time, 50 ng/L was a provisional target value, and testing was not required.
• From October 16, 2023, the town restricted drinking of the water and handed out water from water trucks and in plastic bottles. Preliminary results of emergency testing were 1,100–1,200 ng/L. After changing the water source, cleaning the settling and filtration basins, replacing the activated carbon and cleaning the distribution reservoir, the town lifted the drinking restriction on November 22 (town documents; MLIT case studies).
• The town supplies water from an agricultural dam and water bought from a regional water supply authority, and said it planned to complete work by March 2026 to buy all its water from the authority (case studies, as of November 2024). Whether the work has been completed was not checked for this page.
• On the cause, the town’s documents at the time of the announcement say “unknown.” The town has set up committees, including one to investigate the cause and one on health effects and countermeasures, and keeps posting survey results provided by the prefecture on its website (latest published August 28, 2026).
• There are news reports on blood tests of residents, but the figures could not be confirmed in the town’s public documents, so they are not included here. The Ministry of the Environment says it is difficult to understand or predict health effects on an individual from blood test results at one point in time alone. The ministry’s FAQ also cites Kibichuo Town as a case in which the town compared regional health indicators using existing statistics and reportedly found no difference. → Health effects and blood tests
• The Okayama City Waterworks Bureau (岡山市水道局) reported nd–30 ng/L (highest in FY2023), and Kurashiki City Waterworks 14–48 ng/L (highest in FY2021); for both, the testing points mix the tap, the treatment plant outlet and raw water (before treatment). The prefecture’s four bulk water suppliers were nd except 11 at the Binan Water Supply Authority (備南水道企業団) in FY2022.
• Of the 64 rows for the prefecture, 22 are “raw water only” (such as small water supply systems in Maniwa City (真庭市)), and 10 are suppliers that buy all their water from a bulk supplier. Among private water supplies (for a facility, such as company housing or hospitals), none of the 49 tested in the prefecture was found to exceed the provisional target value (through the end of August 2025).

Timeline

Put it in terms of your own intake

Related explainers

• What happened in areas where high PFAS values were found in tap water? A timeline of Kibichuo, Tama, Okinawa and more
• How does PFAS affect the body? Assessments by different bodies, and what a blood test can tell you
• How do you check PFAS in your local tap water? Reading the national tables and working out “what percent of the TDI”
• Do high PFAS values in rivers or groundwater mean high values in tap water? How guideline values differ from the tap water standard
• Water filters and PFAS

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)
• Kibichuo Town, “Detection of organic fluorine compounds and other substances at the Enjo treatment plant” (updated August 28, 2026)
• Kibichuo Town, “Detection of organic compounds at the Enjo treatment plant (press release of October 17)”
• Kibichuo Town, “Detection of organic fluorine compounds (PFOS, PFOA) at the Enjo treatment plant” (timeline)
• MLIT, “Cases of PFOS and PFOA responses by water suppliers to date” (November 29, 2024), Case 11: Kibichuo Town
• Ministry of the Environment, “Frequently Asked Questions about PFAS,” Q11
• Same follow-up survey, attachment (status of private water supplies by prefecture)
• Ministry of the Environment and MLIT, list of 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.

Other prefectures

• Tottori Prefecture
• Shimane Prefecture
• Hiroshima Prefecture
• Yamaguchi Prefecture