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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.
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.
Our scoring methodology converts raw EPA data into understandable letter grades using a transparent, reproducible process:
We compare each detected contaminant level against EPA Maximum Contaminant Levels (MCLs). Contaminants below 50% of MCL are considered safe, 50-100% are elevated, and above 100% exceed federal limits. More weight is given to health-critical contaminants like lead, arsenic, and bacteria.
We review EPA violation records for the past 5 years, including monitoring failures, treatment technique violations, and MCL exceedances. Recent violations are weighted more heavily than older ones. Systems with no violations receive full points.
We consider water system characteristics including source type (groundwater vs. surface water), system size, and population served. Larger systems typically have more resources for treatment and monitoring.
| Data Type | Frequency | Source |
|---|---|---|
| Contaminant Levels | Quarterly | EPA SDWIS |
| Violations | Monthly | EPA ECHO |
| System Information | Annually | EPA SDWIS |
| City Scores | Quarterly | Calculated |
Each city page displays the last update date. Water quality testing schedules vary by contaminant and water system size, so some data may be 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?