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?
We lay out the formula behind Japan’s tap water standard of “50 ng/L for PFOS and PFOA combined,” how it went from a provisional target value in 2020 to a water quality standard in April 2026, and the values used in the U.S., the EU, the Nordic countries, Canada, Australia and the WHO, side by side with the number of substances covered and whether they are binding.
Short answer
Japan’s standard is 50 ng/L or less for PFOS and PFOA combined. It is calculated from the tolerable daily intake (TDI, the amount considered not to cause adverse health effects even if taken in every day for a lifetime) of 20 ng/kg body weight/day set by the Food Safety Commission of Japan (FSCJ), assuming a body weight of 50 kg, 10% of the TDI allocated to water, and 2 L of water drunk per day.
From April 2020 to March 2026, the same 50 ng/L was a provisional target value (no obligation to test or comply). From April 1, 2026, it became a water quality standard, and water suppliers are now required to test and comply.
The U.S. sets 4.0 ng/L each for PFOA and PFOS, the EU 100 ng/L for the sum of 20 specified PFAS, and Denmark 2 ng/L for the sum of 4. But how many substances are added up, what the value is based on, and whether it is mandatory or a guide differ from country to country, so you cannot call one “lax” or “strict” from the numbers alone.
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.
The formula behind 50 ng/L
According to the Ministry of the Environment, 50 ng/L is derived with the following formula.
| Element | Value | Meaning |
|---|---|---|
| Tolerable daily intake (TDI) | 20 ng/kg body weight/day | Set by the FSCJ on June 25, 2024. 20 each for PFOS and PFOA |
| Body weight | 50 kg | Assumption for the calculation |
| Share allocated to water | 10% | Intake from water is held to this share, allowing for intake from food and other sources besides water |
| Water drunk per day | 2 L | Assumption for the calculation |
| Result | 50 ng/L | 20 × 50 × 10% ÷ 2 |
- By the calculation, PFOS and PFOA each come to 50. Because both are based on “delayed growth in reproduction and development” and are found together in the environment, the Ministry of the Environment took the cautious side and set 50 for the two combined.
- The TDIs are based on effects on the offspring of animals: for PFOS, slower weight gain in pups in a two-generation rat study (uncertainty factor 30); for PFOA, reduced ossification of finger bones in mouse fetuses and earlier sexual maturation in male offspring (uncertainty factor 300).
- For PFHxS, no TDI was set because of “insufficient knowledge for an assessment,” and there is no tap water standard for it. On June 30, 2025, eight substances including PFHxS became “PFAS under consideration” (“要検討 PFAS,” with no target value).
- 1 ng/L is one billionth of a gram in 1 L. 50 ng/L is sometimes written as 0.00005 mg/L.
From provisional target value to water quality standard (2020–2026)
| Period | Event |
|---|---|
| March 2020 | Made an item for water quality management target setting. A provisional target value of 50 ng/L (combined) from FY2020. Water suppliers were to “make efforts” to test; it was not an obligation |
| May 2020 | Made an item requiring monitoring for rivers and groundwater. Guideline value (provisional) of 50 ng/L |
| June 25, 2024 | The FSCJ sets TDIs (20 ng/kg body weight/day each for PFOS and PFOA) |
| February–March 2025 | Public comment (2,734 comments) |
| June 30, 2025 | Ministerial ordinance on water quality standards amended and promulgated. On the same day: a notice setting the specification for mineral water, removal of “provisional” from the guideline value for rivers and groundwater, and designation of eight PFAS under consideration |
| April 1, 2026 | Took effect as a water quality standard. Standard items went from 51 to 52. Testing roughly once every three months or more |
- The value stays at 50. What changed is that testing and compliance became mandatory.
- The Ministry of the Environment writes that “drinking water exceeding the water quality standard does not immediately lead to health damage.” The standard assumes a lifetime of drinking.
- If the standard is exceeded, the supplier investigates the cause and takes steps to lower the concentration. If the exceedance is expected to continue, it is handled as an “abnormal water quality” situation.
Drinking water standards by country: the numbers alone can’t be compared
All values are in ng/L. Always look at them together with the number of substances covered (how many are added up), binding force (mandatory or a guide) and timing (since when).
| Country / body | Substances covered (number) | Value ng/L | Binding force | Timing |
|---|---|---|---|---|
| Japan, tap water | PFOS + PFOA combined (2) | 50 | Mandatory | April 1, 2026 |
| Japan, mineral water | PFOS + PFOA combined (2) | 50 | Mandatory | June 30, 2025 (with transitional measures) |
| U.S. EPA | PFOA (1) and PFOS (1), each | 4.0 | Mandatory | Compliance deadline April 2029 → proposed extension to April 2031 (May 2026) |
| U.S. EPA | PFHxS, PFNA, GenX, each (1) | 10 | Mandatory (rescission proposed) | April 2029 |
| EU | Sum of 20 specified PFAS (20) | 100 | Mandatory | January 12, 2026 |
| EU | PFAS total (all) | 500 | Mandatory (member states choose) | January 12, 2026 |
| Germany | Sum of 20 (20) | 100 | Mandatory | January 12, 2026 |
| Germany | Sum of PFOA, PFNA, PFHxS and PFOS (4) | 20 | Mandatory | January 12, 2028 |
| Denmark | Sum of 4 (4) | 2 | Mandatory | January 1, 2022 |
| Sweden | Sum of 4 (4) | 4 | Mandatory | January 1, 2026 |
| UK (England and Wales) | Sum of 48 specified PFAS (48) | 100 | Guidance | March 2025 |
| Canada | Sum of 25 specified PFAS (25) | 30 | Objective (not binding) | August 9, 2024 |
| Australia | PFOS / PFOA / PFHxS / PFBS, each (1) | 8 / 200 / 30 / 1,000 | Guideline | June 25, 2025 |
| WHO | PFOS and PFOA each / total | 100 / 500 | – (still a 2022 draft, not finalized) | – |
- “Japan is 12 times laxer than the U.S.” is too simple. The U.S. 4.0 was set by assuming there is no threshold for carcinogenicity (a line below which there is no effect), setting the health-based goal at zero, and then deciding based on the lowest concentration that can be reliably measured and the feasibility of treatment. Japan’s 50 is worked back from the TDI. They are set in different ways.
- Japan’s value is for two substances combined. The U.S. sets 4.0 for each one, so adding the two allows up to about 8.
- Denmark’s and Sweden’s 2–4 ng/L are calculated from the tolerable weekly intake for the sum of four substances (4.4 ng/kg body weight/week) set by the European Food Safety Authority (EFSA) in 2020. The health benchmark they start from differs from Japan’s TDI (20 ng/kg body weight/day for one substance), and that difference carries straight through to the standards.
- Canada’s 30 and the WHO draft were set not on health effects but on a precautionary approach based on how far measurement and treatment can go.
- The FSCJ’s assessment report notes that benchmark values used by overseas bodies vary by about 600 times for PFOS and about 5,300 times for PFOA. There is not yet an internationally harmonized assessment.
The U.S. EPA’s 4.0 ng/L: what remains as of October 2026
| Date | Event |
|---|---|
| April 2024 | Final rule announced (Federal Register, April 26). 4.0 each for PFOA and PFOS, 10 each for PFHxS, PFNA and GenX, and a hazard index for a mixture of four substances. Compliance deadline 2029 |
| June 2024 | The American Water Works Association and others sue in court (U.S. Court of Appeals for the D.C. Circuit) |
| May 14, 2025 | EPA announces its plan: keep 4.0 for PFOA and PFOS, move the deadline to 2031, and redo the parts for the other four substances |
| January 2026 | The court denies EPA’s motion to “vacate the four-substance parts.” The 2024 rule remains in effect |
| May 20, 2026 | Two proposed rules published in the Federal Register: (1) water systems that apply can extend the PFOA/PFOS compliance deadline to April 26, 2031 (systems at 12 ppt or above must take short-term reduction measures even during the extension); (2) rescind PFHxS, PFNA, GenX and the hazard index |
| July 20, 2026 | Comment period closes |
| As of October 3, 2026 | No final rule has been issued |
- Both the extension and the rescission are currently “proposals.” They can’t be described as settled, as in “rescinded” or “pushed back to 2031.”
- The 4.0 for PFOA and PFOS itself does not change under either proposal.
- The Ministry of the Environment’s FAQ (updated July 2026) also says that in the U.S., extending the deadline and revisiting substances other than PFOS and PFOA “are being considered.”
The WHO does not yet have a final value
The WHO (World Health Organization) Guidelines for Drinking-water Quality have no finalized value for PFAS.
- The draft put out for comment in September–November 2022 was 100 ng/L each for PFOS and PFOA and 500 ng/L for total PFAS. These values came not from health effects but from detection levels and how far analysis and treatment can go.
- As of September 2025, the WHO says it will “replace it with a broader assessment.”
- The WHO’s advice to member states is “as low as reasonably practicable,” “stop non-essential uses” and “balance this against the risk of water shortages.”
How your area’s value compares with 50 is explained, with the calculation, in How to check PFAS in your local tap water. The basics of PFAS itself are covered in our guide to Teflon and PFAS.
Sources
- Ministry of the Environment, “Overview of the amendment to the ministerial ordinance on water quality standards” (August 2025)
- Food Safety Commission of Japan, “Q&A on the assessment report on organic fluorine compounds (PFAS)”
- Ministry of the Environment, FAQ on PFAS
- U.S. Federal Register, May 20, 2026: proposed extension of the PFOA/PFOS compliance deadline (91 FR 29425)
- U.S. Federal Register, May 20, 2026: proposed rescission for four substances (91 FR 29413)
- European Commission, “New EU rules limit PFAS in drinking water” (January 12, 2026)
- Health Canada: objective for PFAS in drinking water (2024)
- WHO: PFAS in drinking water
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.