About the Data
Where does Clean Water Index get its data?
Clean Water Index pulls data from the EPA Safe Drinking Water Information System (SDWIS) via the Envirofacts API. SDWIS is the federal database that tracks compliance of public water systems with National Primary Drinking Water Regulations. We include active community water systems (CWS) serving 100 or more people.
How often is the data updated?
We refresh our data quarterly from the EPA Envirofacts API. Keep in mind that EPA data itself may lag behind real-time conditions — water systems report violations on varying schedules, and it can take weeks or months for new violations to appear in the federal database.
What counts as a drinking water violation?
A violation occurs when a public water system fails to meet EPA standards set under the Safe Drinking Water Act (SDWA). This includes exceeding Maximum Contaminant Levels (MCLs), failing to apply required treatment techniques, or failing to properly monitor and report water quality results. Not all violations indicate dangerous water — see the next question for details.
What's the difference between health-based and monitoring violations?
A health-based violation means a regulated contaminant was detected above its legally safe limit, or a required treatment technique was not properly applied — these are the most serious type. A monitoring violation means the water system failed to collect required samples, test for contaminants, or submit results on schedule. Monitoring violations do not confirm unsafe water, but they do mean the system is not being properly tracked. Learn more in our guide to EPA violations.
Why doesn't my city appear on this site?
We only include cities with active community water systems recorded in EPA's SDWIS database. Small systems serving fewer than 100 people, private wells, non-transient non-community systems (like schools or offices on their own water supply), and transient systems (like campgrounds) are excluded. If your city isn't listed, it's possible its water system doesn't meet our inclusion criteria or the data wasn't matched to a recognized city name.
Does this data include private wells?
No. The EPA only regulates public water systems — private wells are not covered by the Safe Drinking Water Act and do not appear in SDWIS. If you rely on a private well, you are responsible for testing it yourself. See our guide to well water safety for recommendations.
Understanding Results
My city has violations — is my water safe to drink?
Not necessarily unsafe. Many violations in our data are monitoring or reporting type, meaning the system failed to test or submit results on time rather than actually exceeding a contaminant limit. Our data also represents the full historical record, so old resolved violations are included. Check whether any health-based violations are recent, and read your annual Consumer Confidence Report (CCR) for current water quality details.
What do the safety badges (green/yellow/red) mean?
The color badges are a simplified indicator based on the number of health-based violations in a system's historical record. Green means zero health-based violations on record; yellow means 1–3; red means 4 or more. This is a general guide, not a real-time safety certification — a green badge does not guarantee your water is contaminant-free today.
Why does my city have so many violations?
Our violation counts include the full historical record going back decades, not just recent years. Cities with multiple water systems (for example, large metro areas with several utility districts) will accumulate more violations simply because there are more systems. Many violations shown may have been resolved long ago. Use the violation dates to gauge recency.
What are the most common contaminants found in US drinking water?
The most frequently cited contaminants in EPA violation data include disinfection byproducts (total trihalomethanes/TTHM and haloacetic acids/HAA5), coliform bacteria, nitrate, lead, and arsenic. These vary significantly by region and water source type. Read our guide to common contaminants and health effects for a full breakdown.
What is an MCL (Maximum Contaminant Level)?
An MCL is the legally enforceable maximum concentration of a specific contaminant allowed in public drinking water. The EPA sets MCLs based on the health effects of the contaminant, the feasibility of treatment technologies available, and cost-benefit analysis. When water exceeds an MCL, the system is in violation and must notify customers and take corrective action.
Are there contaminants in my water that aren't shown here?
Yes. The EPA currently regulates about 90 contaminants under the SDWA, but thousands of other chemical and biological substances can be present in drinking water. PFAS ("forever chemicals"), pharmaceuticals, microplastics, and many industrial chemicals may be present but are not always required to be tested for under current rules. This site reflects only what the EPA monitors and enforces.
Taking Action
How can I get my water tested?
For basic information, contact your local water utility — they are required to test regularly and provide results. For independent testing, hire a state-certified laboratory, which typically costs $50–$200 depending on the contaminants tested. Make sure to specify what you want tested based on your concerns. Our guide to reading water quality reports can help you understand your results.
What type of water filter should I buy?
The right filter depends on which contaminants you want to remove. NSF/ANSI Standard 53 certified filters are effective for lead and volatile organic compounds. Reverse osmosis (RO) systems provide the most comprehensive filtration. For PFAS, look for NSF P473 certification specifically. Our guide to filtering tap water explains the options in detail.
Where can I find my water utility's annual water quality report?
This report is called a Consumer Confidence Report (CCR). Water utilities are required to deliver it to customers annually by July 1. Check your utility's website, call them directly to request a copy, or use the EPA's online CCR search tool at epa.gov. The CCR lists every regulated contaminant tested in the past year, the levels found, and the legal limits.
Who should I contact if I think my water is unsafe?
Start with your local water utility — they can tell you what is currently in the water and what actions are being taken. If you are not satisfied, escalate to your state drinking water program (every state has one). For federal-level concerns or to report violations, contact the EPA Safe Drinking Water Hotline at 800-426-4791 (Monday–Friday, 10am–4pm Eastern).
Is bottled water safer than tap water?
Not necessarily. Bottled water is regulated by the FDA, which sets standards similar to — but in some cases less stringent than — EPA standards for tap water. Some bottled water is simply filtered tap water. The environmental cost of single-use plastic bottles is significant. For most people, a well-chosen filter on tap water provides comparable or better quality at a fraction of the cost and environmental impact.
How can I protect my family from water contamination?
Run cold water for 30–60 seconds before drinking if your home has older plumbing, since lead can leach from pipes and fixtures. Use an NSF-certified filter appropriate for your area's known contaminants. Get your water independently tested if you have concerns. Read your annual CCR to stay informed about what's in your local supply. Our guide to protecting your family covers these steps in detail.