PFAS in tap water: Saitama 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

• Fujimi City’s annual maximums were 21, 22, 49, 36 and 13 (FY2021–FY2025). It measures both at the treatment plant outlet and in raw water (water before treatment at the plant), and the table does not show which one the listed values come from.
• Fukaya City went nd, nd, nd, 6 and 9, then 43 in FY2025. The FY2025 value covers through the end of August.
• Others above 25 ng/L were Shiki City (志木市) at 31 (FY2024; nd in other years) and Hatoyama Town (鳩山町) at 30 (FY2021, raw water only). Sayama City (狭山市) was nd–23 and Honjo City (本庄市) 9–19.
• The Saitama City Waterworks Bureau (さいたま市水道局) was 3–9 (treatment plant outlet and raw water), and the prefectural bulk water supplier (the Saitama Prefectural Public Enterprise Bureau (埼玉県企業局)) was 3–7. Kawaguchi City (川口市) was 7–9 and Tokorozawa City (所沢市) 3–8.
• Values from utilities that measure only in raw water (such as Higashimatsuyama City (東松山市), Fujimino City (ふじみ野市), Hidaka City (日高市) and Hatoyama Town) are not the values of tap water. For Yoshimi Town (吉見町) and Namegawa Town (滑川町), which buy all their water from a bulk supplier (they buy water from another utility), check the supplier’s values as well. → How to read the national table
• Private water supplies (for facilities such as company housing and hospitals) were tested at 167 of the 338 operators, and no exceedance has been confirmed (through the end of August 2025).
• The national table shows “the highest value for each utility in that fiscal year.” In cities with several treatment plants, values differ by system. From April 2026 this becomes a water quality standard, and periodic testing is, in principle, required roughly once every three months or more often (small water supply systems can test less often based on past results, and utilities that buy all their water from a bulk supplier can skip it under certain conditions). → How was the “50 ng/L” standard decided?

Put it in terms of your own intake

Related explainers

• How do you check PFAS in your local tap water? Reading the national tables and working out “what percent of the TDI”
• Japan’s PFAS standard for tap water, “50 ng/L”: how was it set, and how does it differ from the U.S. and EU?
• Do high PFAS values in rivers or groundwater mean high values in tap water? How guideline values differ from the tap water standard
• How does PFAS affect the body? Assessments by different bodies, and what a blood test can tell you
• Water filters and PFAS

Sources

• Ministry of the Environment and MLIT, “Results of the follow-up survey on PFOS and PFOA in water supplies” (December 25, 2025)
• Same, list of survey results (updated), Excel (annual maximums, FY2020–FY2025)
• Ministry of the Environment and MLIT, list of survey results, Excel (published November 29, 2024; sampling point column)
• Same, follow-up survey annex (status of private water supplies by prefecture)
• Ministry of the Environment, notice on the enforcement of the partial revision of the Ministerial Ordinance on Water Quality Standards, etc. (No. 2506301, June 30, 2025)

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

• Ibaraki Prefecture
• Tochigi Prefecture
• Gunma Prefecture
• Chiba Prefecture
• Tokyo
• Kanagawa Prefecture