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.
PFAS Water Quality Report
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 in Los Gatos, California · jackzacey@gmail.com
State Comparison Table
Compare represented UCMR 5 detections and water systems across states.
This tool is built on EPA UCMR 5 public drinking-water monitoring data (2023–2025). The processed detection-only dataset contains 40,311 compound-level records across 14,071 ZIP codes, 4,885 represented public water systems, and 12 analytes.
EPA records were linked to ZIP codes using Public Water System Identifiers. Non-detections were excluded, and the highest observed concentration was retained for each compound–ZIP pair. A water-system record can map to several ZIP codes. These are observed monitoring results—not modeled exposure estimates or regulatory compliance determinations. Read the complete processing method and threshold rules →
The analytic denominator includes only ZIP codes with retained detections. Small systems, rural communities, and private wells are not comprehensively represented. Displayed values are the highest observations from 2023–2025, not long-term averages or measurements at a particular household tap. A ZIP code returning no result must not be interpreted as contamination-free.
PFAS Estimator is an independent, student-led project created by Jack Zhang. Clinical and epidemiologic review is in progress with Joshua Tamayo-Sarver, MD, PhD. The project is not institutionally endorsed and has not yet completed journal peer review or formal independent validation. Full review status →
| Compound | Comparison Value | 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 HI reference | 5,009 (36% of all ZIPs) | Hazard Index not calculated | 0.0087 µg/L | 0.2900 µg/L |
- Analysis of EPA UCMR 5 data (2023–2025) found that 36% of ZIP codes in this detection-only dataset had at least one regulated PFAS compound at or above its applicable federal comparison value (5,059 of 14,071 ZIP codes). The analysis retains the highest observed value per compound–ZIP pair; it does not reproduce formal regulatory compliance calculations.
- 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 (635 of 2,999 zip codes with PFHxS detections).
- PFOS was the most widely detected regulated compound, appearing in 29% of all zip codes in the dataset (4,083 of 14,071). Peak detected level: 0.490 µg/L, more than 120 times the federal limit of 0.004 µg/L.
- PFOA peak detected level was 0.235 µg/L, nearly 60 times the federal limit of 0.004 µg/L.
- Lithium was the most prevalent analyte overall, detected in 57% of the 14,071 ZIP codes in the dataset. Lithium has no federal MCL; the project's 7.36 µg/L comparison is research-based, not regulatory.
- PFBS was detected in 5,009 ZIP codes. No individual PFBS exceedance rate is reported because the federal comparison is a mixture Hazard Index requiring co-located sample-event values that this aggregated dataset does not retain.
PFAS Detections by State. Based on EPA UCMR 5 data across 14,071 zip codes. Click a column to sort.