PFAS in tap water: Ibaraki 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 Koda-Higashi small water supply association showed “none” for testing record in the November 2024 table, and its value appeared for the first time in the 2025 table. The table does not say where it was sampled (tap, treatment plant or raw water).
• Among utilities that measure at the tap, Chikusei City (筑西市) had 31 (FY2022), Namegata City had 30 (FY2024), and Omitama City (小美玉市) had 20, 21 and 26 (FY2023–FY2025). Omitama City’s values are rising little by little.
• The prefecture’s bulk water suppliers (utilities that sell water wholesale to cities and towns) were 8–13 for Rokko Regional (鹿行広域), 5–10 for Kennansei Regional (県南西広域), and nd–2 for Kenchuo Regional (県中央広域) (measured at the treatment plant outlet and in raw water).
• Nine utilities buy all their water from a bulk supplier (they buy water from another utility), including Tsukuba City (つくば市), Tsuchiura City (土浦市) and the Ibaraki Kennan Water Supply Authority (茨城県南水道企業団). There are years in which they did not test the water themselves, so check the supplier’s values as well. → How to read the national table
• Private water supplies (for a facility) were tested at 159 of the 225 operators, and 2 exceedances have been confirmed. The national-government one is the private water supply of Ibaraki Nogei Gakuin (茨城農芸学院), at 61 ng/L in raw water (water before treatment at the plant). According to the national documents, it is being handled with water filters as an emergency measure and is planned to switch to the public water supply.

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”
• Do high PFAS values in rivers or groundwater mean high values in tap water? How guideline values differ from the tap water standard
• 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?
• 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; national-government private water supplies above the provisional target value)

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

• Tochigi Prefecture
• Gunma Prefecture
• Saitama Prefecture
• Chiba Prefecture
• Tokyo
• Kanagawa Prefecture