U.S. Tap Water PFAS Checker

Enter your zip code to find out what's in your tap water, what it means for your health, and what you can do about it.

How to read these results: Ingesting tap water — drinking it, cooking with it, making coffee or baby formula — is the primary route of PFAS exposure for most people. Skin absorption during showering is minimal by comparison. Detection means a compound was measurable in your water system. Detection doesn't mean your water is immediately dangerous — but it does mean you deserve to know what's there and what the research says.

This report summarizes PFAS compounds detected in your public water system based on federal EPA monitoring data. Bring this to your next appointment to discuss with your healthcare provider. Detection does not indicate a health risk — context and levels matter.

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Why tap water ingestion matters

Drinking tap water and cooking with it are the primary ways PFAS compounds enter the body. Unlike skin contact during bathing — where absorption is minimal — ingestion allows these compounds to pass directly into the bloodstream. Because PFAS are resistant to breakdown, they accumulate in the body over time. Small, repeated exposures through daily tap water use can build up across months and years, which is why chronic low-level ingestion is the focus of most public health research.

This matters most during periods when the body is especially sensitive to hormonal changes — including pregnancy, when thyroid hormones produced by the mother are essential for fetal brain development before the fetal thyroid becomes functional around week 12. Researchers continue to study whether long-term PFAS ingestion at levels currently considered acceptable may still carry health implications for vulnerable populations.

This tool draws on federal EPA monitoring data to make that information accessible to anyone curious about their community's tap water. If something concerns you, the most productive next step is a conversation with your doctor and your local water utility.

Built by Jack Zhang · jackzacey@gmail.com

Data from the EPA Unregulated Contaminant Monitoring Rule (UCMR 5), 2023–2025. Covers U.S. water systems with documented PFAS detections. Detection does not indicate a health risk. Not medical advice. · EPA Source

For Researchers & Journalists

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This tool is built on EPA UCMR 5 data (2023–2025), the most comprehensive federal PFAS drinking water dataset ever collected. The dataset covers 14,071 U.S. zip codes and 40,311 compound-level detections processed from two raw EPA monitoring files totaling approximately 1.9 million rows.

Dataset methodology
Raw EPA files were joined to zip code mapping via PWSID (Public Water System ID). Non-detections were filtered out. Where a compound appeared multiple times for the same zip code, the highest recorded level was kept. Output: one entry per compound per zip code.

Known limitations
Systems serving fewer than 3,300 people participated voluntarily — rural and small-town America is underrepresented. Data reflects a monitoring snapshot (2023–2025), not continuous measurement. Private wells (43 million Americans) are entirely absent. A zip code returning no results may mean clean water, an untested system, or a system below the reporting threshold. Detection levels reflect output at the treatment plant, not at the tap.

How to cite
Zhang, J. (2025). U.S. Tap Water PFAS Checker [Web tool]. Data source: U.S. EPA UCMR 5 (2023–2025). jackzacey.github.io/pfas-estimator

📊 National Finding — Headline Stat

36% of zip codes in this dataset

had at least one PFAS compound detected above its EPA limit — across 5,059 of 14,071 zip codes with confirmed detections.

Compounds with EPA Limits — Prevalence & Exceedance

Source: EPA UCMR 5 (2023–2025) · 14,071 zip codes nationally.

Compound	EPA Limit	Zips Detected	Note	Avg Level	Peak
PFOS	0.004 µg/L	4,083 (29% of all zips)	All recorded detections at or above limit	0.0120 µg/L	0.4900 µg/L
PFOA	0.004 µg/L	3,936 (28% of all zips)	All recorded detections at or above limit	0.0095 µg/L	0.2350 µg/L
HFPO-DA	0.010 µg/L	203 (1.4% of all zips)	35% of detections above limit	0.0209 µg/L	0.1400 µg/L
PFNA	0.010 µg/L	558 (4% of all zips)	35% of detections above limit	0.0096 µg/L	0.0998 µg/L
PFHxS	0.010 µg/L	2,999 (21% of all zips)	21% of detections above limit	0.0088 µg/L	0.2502 µg/L
PFBS	2.000 µg/L	5,009 (36% of all zips)	No detections above limit	0.0087 µg/L	0.2900 µg/L

PFOA and PFOS are reported by prevalence rather than exceedance rate. UCMR 5 records detections at or above the minimum reporting level, which for these compounds aligns with the 0.004 µg/L EPA limit — making a meaningful exceedance percentage impossible to calculate from this dataset alone.

Key findings (citable)

Analysis of EPA UCMR 5 data (2023–2025) across 14,071 U.S. zip codes found that 36% had at least one PFAS compound detected above its federal limit.
PFHxS — which has an estimated 8-year biological half-life and the strongest documented thyroid disruption signal among regulated PFAS — exceeded EPA limits in 21% of zip codes where it was detected, across 2,999 zip codes nationally.
PFOS was the most widely detected regulated compound, appearing in 29% of all zip codes in the dataset (4,083 of 14,071).
Lithium — currently under EPA review with a regulatory decision expected in 2026 — was the most prevalent contaminant overall, detected in 57% of zip codes in the dataset with no federal limit yet established.
PFBS was detected in the most zip codes of any regulated compound (5,009) yet had zero exceedances of its 2.0 µg/L limit — a counterpoint showing not all detections signal risk.

PFAS Detections by State — Based on EPA UCMR 5 data across 14,071 zip codes. Click a column to sort.

U.S. Tap Water PFAS Checker

PFAS Water Quality Report

Why tap water ingestion matters

For Researchers & Journalists