Idaho PFAS results from EPA's final data

Report published Nov 14, 2026 · EPA UCMR 5 final data file of Oct 15, 2026 (samples collected 2023–2025) · Method · National results →

2 Idaho water systems serving 21,500 people had PFAS above a 2024 federal limit in EPA's final round of nationwide PFAS testing: 3% of the 61 Idaho systems tested, compared with 11% nationally.

systems tested (serving 1.3 million people)

had at least one PFAS detected

had an average above a federal limit

21,500

people served by those systems

Highest PFOA or PFOS averages in Idaho

Garden City Water and Sewer System Garden City · PFOS
25.5 ppt
Capitol Water Corp Boise City · PFOS
9.45 ppt
Meridian Water Dept Meridian · PFOS
2.45 ppt

The 3 Idaho systems with the highest PFOA or PFOS entry-point average (whichever is higher) in EPA's 2023–2025 testing, in parts per trillion.

Chart data as a table

System	ppt
Garden City Water and Sewer System · Garden City · PFOS	25.5
Capitol Water Corp · Boise City · PFOS	9.45
Meridian Water Dept · Meridian · PFOS	2.45

Largest systems above a limit

#	System	People served	Above the limit for	PFOA avg	PFOS avg
1	Garden City Water and Sewer System Garden City Above: PFOS, PFHxS, Hazard Index	12,500	PFOS, PFHxS, Hazard Index	–	25.5 ppt
2	Capitol Water Corp Boise City Above: PFOA, PFOS, PFNA, Hazard Index	9,000	PFOA, PFOS, PFNA, Hazard Index	5.8 ppt	9.45 ppt

Which limits were exceeded

PFAS	Federal limit	Systems above it	People served
PFOA 9,000 people	4 ppt	1	9,000
PFOS 21,500 people	4 ppt	2	21,500
PFHxS 12,500 people	10 ppt	1	12,500
PFNA 9,000 people	10 ppt	1	9,000
GenX (HFPO-DA)	10 ppt	0	0
Hazard Index 21,500 people	1	2	21,500

"–" in the table above means not detected. A system can be above more than one limit. EPA proposed in May 2026 to rescind the PFHxS, PFNA, GenX and Hazard Index limits. That proposal is not final.

Data and how to cite it

Download every Idaho water system as CSV (PFOA and PFOS averages, systems above a limit, lead, violations).
EPA's source file: UCMR 5 occurrence data.

Suggested citation:

Tap Water Results, "Idaho PFAS results from EPA's final UCMR 5 data" (published Nov 14, 2026, EPA data file of Oct 15, 2026). https://tapwaterresults.com/pfas/idaho/

You're welcome to quote and republish these figures with a link back. Questions from reporters: see contact.

Method

For each system we average each entry point's UCMR 5 results (non-detects count as zero, complete sets of samples only) and compare the highest entry-point average with the 2024 federal limit, using EPA's rounding. This is how EPA compares UCMR 5 results to the limits in its own data summary, and our national counts match EPA's published table within 2% (how we check). Results are monitoring data from 2023–2025, not compliance determinations, and treatment installed since then is not reflected. Full method.

Questions

How many Idaho water systems have PFAS above the limit?

2 of the 61 Idaho community water systems EPA tested in 2023–2025 (3%) had at least one entry-point average above a 2024 federal PFAS limit. They serve 21,500 people. Nationally the share is 11%.

Are these systems violating the law?

Not yet. Systems have until 2029 to meet the 2024 limits, and EPA has proposed moving the PFOA and PFOS deadline to 2031 and rescinding the other limits. EPA's UCMR 5 results are monitoring data and do not determine compliance.

Which systems were tested?

EPA's UCMR 5 tested every community water system serving more than 3,300 people and a representative sample of smaller ones. Systems that were not tested have no federal result, which is not the same as having no PFAS.

All Idaho water systems → · National results → · PFAS results for every state →

Source: U.S. EPA drinking water records and PFAS testing (UCMR 5). How we read the data.