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Transparency in how we collect, process, and present water quality information for communities across the United States. Our analysis combines official EPA data with health guidelines from leading environmental organizations.
All water quality data on US Water Grade comes from official government sources. We aggregate and present publicly available data to make it more accessible to consumers. The grades on city, state and comparison pages are computed from four EPA bulk datasets: the SDWIS violations and enforcement file and the Lead and Copper Rule sample file (both from EPA ECHO, 2026Q2 extract dated 2026-07-09), the UCMR5 PFAS occurrence file (2023–2026, July 2026 release) and the Six-Year Review 4 compliance-monitoring files (2012–2019, released March 2024). Cities are joined to a water system through the utility's PWSID.
Our primary data source. SDWIS is the EPA's official database containing information about public water systems and their compliance with drinking water regulations. It includes water quality testing results, violation records, and enforcement actions for all 150,000+ public water systems in the United States.
Learn more about SDWISProvides detailed compliance and enforcement data for water systems, including inspection results, violation severity, and enforcement actions taken. ECHO data helps us understand the compliance history of each water system.
Visit EPA ECHOAnnual water quality reports that water utilities are required by law to provide to their customers. CCRs contain detailed information about water source, detected contaminants, and how levels compare to EPA standards. We reference CCR data to supplement SDWIS information.
About Consumer Confidence ReportsState environmental and health agencies administer drinking water programs and maintain additional data on water systems within their jurisdictions. State data supplements federal databases and provides local context.
While EPA sets legal limits, the Environmental Working Group provides science-based health guidelines that are often more stringent. EWG's recommendations are based on the latest peer-reviewed research and consider long-term health effects, especially for vulnerable populations like children and pregnant women. We reference EWG guidelines alongside EPA limits to give you a complete picture of potential health risks.
Visit EWG Tap Water DatabaseWe incorporate health effect information from the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) guidelines. These authoritative sources provide evidence-based health information about contaminant exposure risks, vulnerable populations, and recommended protective measures.
When evaluating water quality, we consider both EPA legal limits and EWG health guidelines. Understanding the difference helps you make informed decisions about your water.
| Contaminant | EPA MCL | EWG Health Guideline | Why the Difference? |
|---|---|---|---|
| Lead | 15 ppb (action level) | 1 ppb | No safe level; any exposure affects children's brain development |
| Arsenic | 10 ppb | 0.004 ppb | EPA limit set in 2001; cancer research shows lower levels needed |
| PFOA/PFOS | 4 ppt (2024) | 1 ppt | Forever chemicals persist in body; lower is safer |
| Chromium-6 | 100 ppb (total chromium) | 0.02 ppb | EPA has no specific limit; EWG based on California research |
| Total THMs | 80 ppb | 15 ppb | Disinfection byproducts linked to cancer at lower levels |
Important: EPA Maximum Contaminant Levels (MCLs) are legally enforceable limits that balance health protection with what's economically feasible for water utilities. EWG guidelines represent levels associated with minimal health risk based on current science. Both are valuable reference points for understanding your water quality.
We track contaminants regulated under the Safe Drinking Water Act, organized into categories:
Lead, arsenic, copper, nitrates, fluoride, chromium, mercury, and other metals and minerals from natural deposits or industrial discharge.
Trihalomethanes (THMs), haloacetic acids, bromate, and other chemicals formed when disinfectants react with organic matter in water.
Total coliform, E. coli, Giardia, Cryptosporidium, and other bacteria, viruses, and parasites that can cause illness.
PFAS (forever chemicals), benzene, atrazine, and other carbon-based compounds from industrial processes, agriculture, or other sources.
Radium, uranium, gross alpha, and gross beta particles from natural sources or human activities.
Chlorine, chloramine, and chlorine dioxide used to kill harmful microorganisms in drinking water.
In force since September 2026 · data files generated 2026-09-13
Every graded city starts at 100 points and loses points only for findings that appear in EPA's own records for its public water system. Nothing is estimated, modelled or inferred from infrastructure age. The letter is a fixed band: A ≥ 90 · B ≥ 80 · C ≥ 70 · D ≥ 60 · F below 60.
| What we look at | Rule | Points |
|---|---|---|
| Health-based violations | Each MCL, MRDL or treatment-technique violation with a compliance period in the last 5 years (SDWIS 2026Q2) | −10 each, capped at −40 |
| Unresolved health-based violation | Any health-based violation since 2016 still Unaddressed or Addressed (not Resolved/Archived) | −20 flat |
| Monitoring & reporting violations | Missed samples or late reports in the last 5 years — paperwork, not measured contamination | −1 each, capped at −10 |
| Lead at the tap | Most recent Lead and Copper Rule 90th-percentile result, only if its monitoring period ends 2020 or later | ≥15 ppb −25 · ≥10 ppb −10 · ≥5 ppb −3 |
| PFOA / PFOS | Highest UCMR5 (2023–2026) result at or above EPA's 4 ppt MCL | −10 each |
| Other PFAS | Any other PFAS compound detected above its reporting limit in UCMR5 | −2 each, capped at −6 |
| Historical monitoring 2012–2019 (SYR4), MCL analytes | Arsenic, nitrate, fluoride, chromium, uranium, radium, gross alpha: finished-water samples over the MCL | >5% of samples over −10 · any over −3 · average >80% of MCL −2 |
| Historical monitoring 2012–2019 (SYR4), TTHM & HAA5 | Disinfection byproducts are regulated as a locational running annual average, so we score the average only; single high samples are reported but never penalised | average > MCL −10 · average >80% of MCL −3 |
| SYR4 cap | Total historical-monitoring penalty is capped because the data is 7–14 years old | cap −20 |
| Lead & copper tap samples (SYR4) | Shown for context; compliance is on the 90th percentile above | never scored |
The first real-data rubric penalised single TTHM/HAA5 samples above the MCL (−10 per analyte) and PFOA/PFOS at −15 each, which pushed 151 of 760 cities to an F mostly on historical byproduct spikes. Because the disinfection-byproduct MCL is a running annual average, v2 scores the 2012–2019 average instead, caps the total historical penalty at −20, and trims the PFAS deductions. Health-based violations are now capped at −40 so one bad year cannot zero a system on its own.
The rubric is implemented in one place (scripts/real/grade.ts) and every “Why this grade” list on a city page is the literal output of that function, so what you read is what was scored. See a city's page for its reasons, or the state rankings for the distribution.
| Data Type | Frequency | Source |
|---|---|---|
| Violations & enforcement | Quarterly (currently SDWIS 2026Q2, file dated 2026-07-09) | EPA ECHO SDWA bulk download |
| Lead & copper 90th percentiles | Quarterly (same SDWIS extract) | EPA ECHO SDWA_LCR_SAMPLES |
| PFAS occurrence | Quarterly EPA releases through 2026 (currently July 2026, covering Jan 2023 – Jun 2026) | EPA UCMR5 |
| Historical contaminant samples | Every six years (2012–2019 set released March 2024; next set expected ~2030) | EPA Six-Year Review 4 |
| City scores | Recomputed whenever any input file is refreshed | Calculated (rubric v2) |
Each city page names the dataset and period behind every table. Sampling schedules vary by contaminant and system size — large systems test lead every three years on reduced monitoring, small systems sampled PFAS only twice under UCMR5 — so some figures are more recent than others.
Our data reflects water quality at the treatment plant or distribution system. Your home's water may differ due to plumbing age, pipe material (especially lead service lines), or fixtures. Homes built before 1986 may have lead pipes or solder.
Not all contaminants are tested regularly. Some emerging contaminants like PFAS may be under-reported in many areas because testing is not yet required everywhere. Testing frequency varies by contaminant and system size.
Some EPA Maximum Contaminant Levels (MCLs) have not been updated in decades despite new scientific research. Meeting federal limits does not guarantee zero health risk. Some health organizations recommend stricter guidelines for certain contaminants.
Our data covers public water systems only. If you have a private well, this data does not apply to your water. Private well owners should test their water regularly through a certified laboratory.
Vulnerable populations including infants, pregnant women, elderly individuals, and those with compromised immune systems may need stricter water quality standards. Consult with healthcare providers for personalized guidance.
Contact your water utility to request your annual Consumer Confidence Report (CCR). This is your official local water quality report, required by law.
Visit echo.epa.gov and search for your water system to see official compliance and violation data.
For the most accurate picture of what's coming out of your tap, consider having your water tested by a certified laboratory. This is especially important if you have older plumbing or are in a vulnerable population.
Your local water utility is the authoritative source for information about your specific water supply. They can answer questions about source, treatment, and any ongoing issues.
This website is for informational purposes only and is not health advice.
The information provided on US Water Grade is intended to help you understand publicly available water quality data. It should not be used as a substitute for professional medical advice, diagnosis, or treatment.
If you have health concerns related to your water quality, please consult with a healthcare provider. For official water quality information, contact your local water utility directly.
Have questions about our data sources, scoring methodology, or how to interpret water quality information? We welcome your feedback and inquiries.
Contact UsThe safety of your tap water depends on your location and water system. While most public water systems in the United States meet EPA safety standards, water quality varies significantly between cities. Some areas have elevated levels of contaminants like lead, PFAS, or arsenic that may pose health risks. We recommend checking your specific city's water quality report on our site and reviewing your utility's annual Consumer Confidence Report (CCR) for detailed information about what's in your tap water.
Have more questions about water quality?