EWG Tap Water Database: The Complete Guide

Last updated: February 2026

What Is the EWG Tap Water Database?

The EWG Tap Water Database is a free online tool maintained by the Environmental Working Group, a nonprofit environmental health organization. It aggregates drinking water quality data from over 50,000 water utilities serving more than 280 million Americans — making it the most comprehensive public database of its kind.

The database pulls from testing data that utilities are legally required to report to state environmental agencies and the EPA. EWG collects, standardizes, and presents this information in a searchable format so ordinary citizens can understand what's in their local drinking water without sifting through technical regulatory filings.

What makes the EWG database different from government sources isn't the underlying data — it's the analysis layer. EWG compares detected contaminant levels not just against EPA legal limits, but against their own stricter health guidelines based on current peer-reviewed science. This often reveals a stark picture: water that is perfectly "legal" may contain contaminants at levels that independent researchers consider potentially harmful.

How to Use the Database Step-by-Step

Using the EWG Tap Water Database is straightforward. Here's exactly how to check your water:

Step 1: Go to EWG's Website

Navigate to ewg.org/tapwater. You'll land on the database homepage with a prominent search bar.

Step 2: Enter Your Zip Code

Type your zip code into the search field and hit enter. If you're searching for a specific utility (useful if you want to check a city you're moving to), you can also search by utility name or city.

Step 3: Select Your Utility

Multiple utilities may serve the same zip code, especially in suburban areas. Your water bill will identify your specific utility — usually listed as a water authority or municipal water department. Select the correct one from the dropdown list.

Step 4: Review the Summary Dashboard

The first screen shows a summary card for your utility including:

• Total number of contaminants detected
• Number of contaminants exceeding EWG health guidelines
• Number of contaminants exceeding EPA legal limits
• A letter-grade-style rating (if applicable)
• The most recent testing period covered

Step 5: Click "See All Contaminants"

The full contaminant list shows every substance detected with its measured concentration, the EPA legal limit, and the EWG health guideline. Color coding makes it easy to spot which contaminants are at concerning levels.

Step 6: Click Individual Contaminants for Detail

Each contaminant links to a detailed page explaining what it is, where it comes from, its health effects, and how many Americans are exposed at that level.

How to Read Your Results

Understanding what the numbers mean is the most important part of using the database. Here's how to interpret each column:

Detected Level

The concentration of the contaminant found in your utility's water, usually expressed in parts per billion (ppb), parts per trillion (ppt), or milligrams per liter (mg/L). This is typically an average of multiple tests taken over the reporting period.

EPA Legal Limit (MCL)

The Maximum Contaminant Level — the legally enforceable threshold. If your utility's water is below this number, they're in compliance with federal law. This does not necessarily mean the water is free of health risk.

EWG Health Guideline

EWG's own threshold, based on what current independent science says is the "no appreciable risk" level. For carcinogens, this is often calculated as the concentration associated with a 1-in-a-million cancer risk — a standard used by the EPA itself for other environmental regulations.

Times Over Limit / Health Guideline

EWG expresses the gap as a multiplier — e.g., "12x the EWG health guideline." This puts the numbers in human terms. A contaminant at 48x the health guideline is more concerning than one at 2x, even if both are "legal."

EWG Health Guidelines vs. EPA Legal Limits: Why They Differ So Much

The gap between EWG's guidelines and EPA's limits can seem alarming — and understanding why they differ is essential context.

The EPA sets its Maximum Contaminant Levels through a process that explicitly balances health risk against cost and technical feasibility. The Safe Drinking Water Act requires the EPA to consider what treatment technologies can achieve and what utilities can afford when setting enforceable limits. This is a policy decision, not purely a scientific one.

EWG's health guidelines, by contrast, are derived solely from health research — specifically the concentration associated with a 1-in-1,000,000 lifetime cancer risk for carcinogens, or the lowest observed adverse effect level for non-carcinogens. These are the same risk thresholds the EPA uses in other regulatory contexts.

The key takeaway: when EWG shows a contaminant "exceeds health guidelines," it doesn't mean your water is acutely dangerous or that you should stop drinking it immediately. It means long-term exposure at that concentration may carry a health risk based on the best available science — even if regulators have deemed those levels legally acceptable.

Most Common Contaminants Found in the EWG Database

Based on EWG's national data analysis, here are the contaminants most likely to appear in your report:

1. Disinfection Byproducts (HAAs and THMs)

These are found in virtually every chlorinated water system in the United States. When utilities add chlorine to kill pathogens, it reacts with naturally occurring organic matter to form haloacetic acids (HAAs) and trihalomethanes (THMs). Both are probable or known carcinogens at high exposure levels.

HAAs and THMs almost always appear "above EWG health guidelines" but "below EPA legal limits" — this is one of the most common entries in the database.

2. Chromium-6

EWG found chromium-6 in the tap water of utilities serving over 218 million Americans. There is currently no federal MCL specific to chromium-6. California set the only state-level limit at 10 ppb — which EWG considers far too permissive given that chromium-6 is a known carcinogen.

3. Nitrates

Common in agricultural areas due to fertilizer and manure runoff. The EPA limit of 10 mg/L was set primarily to prevent acute "blue baby syndrome" in infants — but newer research links lower levels to thyroid disorders, colorectal cancer risk, and pregnancy complications.

4. Arsenic

A natural contaminant in groundwater, particularly in the western U.S., New England, and parts of the Midwest. The EPA's 10 ppb limit is among the least protective of any major contaminant — the EWG health guideline is 0.004 ppb, 2,500 times stricter.

5. Lead

Unlike source-water contaminants, lead enters water after it leaves the treatment plant — through aging service lines and household plumbing with lead solder. The EWG database may underreport lead because utilities test from specific faucets under ideal conditions, not average household plumbing.

6. PFAS (Forever Chemicals)

Per- and polyfluoroalkyl substances are increasingly appearing in EWG database reports as utilities improve their testing. The EPA issued the first-ever enforceable PFAS limits in 2024. Read our full PFAS guide →

7. Radium

Naturally radioactive element found in groundwater. Carcinogenic with long-term exposure. Common in parts of the South, Midwest, and Mountain West.

Limitations of the EWG Database You Should Know

The EWG database is an invaluable tool, but it has real limitations that affect how you should interpret results:

1. It Reflects Treatment Plant Output, Not Your Tap

The most important limitation: utility testing happens at treatment plants and monitored distribution points — not from your specific faucet. Lead, for example, primarily enters water from your home's pipes, not from the source. A utility's "legal" lead level can coexist with dangerously high lead at individual taps in older homes.

2. Testing Data Can Be Several Years Old

Utilities test on schedules mandated by regulation, which vary by contaminant. Some are tested annually, others every few years. The data in your EWG report may be 2–5 years old. Water quality can change significantly due to infrastructure changes, droughts, or new pollution sources.

3. Private Wells Are Not Included

Approximately 43 million Americans get water from private wells, which are not regulated by the EPA or tested by utilities. These wells don't appear in the EWG database. If you use a private well, you need to test it independently — ideally once a year.

4. Not All Contaminants Are Tested

The EPA requires testing for about 90 contaminants. There are thousands of chemicals in industrial use that could theoretically contaminate water but aren't routinely tested. PFAS is the most prominent example — utilities only recently began testing for these compounds.

5. Average Concentrations Hide Peaks

Reported values are averages across multiple tests. Seasonal peaks — such as higher nitrates after heavy rain and agricultural runoff — may be significantly higher than the annual average shown in the database.

What to Do If Your Water Has High Contaminants

Finding contaminants above EWG health guidelines in your report is common and doesn't require panic. Here's a practical action plan:

Step 1: Identify Your Priority Contaminants

Not all contaminants warrant the same urgency. Prioritize:

• Lead — especially if you have children under 6, are pregnant, or live in a home built before 1986
• PFAS — if near military bases, airports, or industrial facilities
• Nitrates — if you have infants under 6 months, are pregnant, or have thyroid issues
• Arsenic — if your utility shows levels above 5 ppb
• Disinfection byproducts — relevant for everyone but especially concerning during pregnancy

Step 2: Get a Home Test for Confirmation

Because the EWG database reflects plant output, not your tap, consider testing your actual drinking water — especially for lead. A comprehensive home test kit will tell you what's coming out of your specific faucet.

Step 3: Choose the Right Filter

The right filtration depends on which contaminants you need to target. See our filter comparison below, or jump to our full filter guide.

Step 4: Contact Your Utility if Levels Are Very High

If your report shows contaminants significantly exceeding EPA legal limits, contact your water utility directly. They are legally required to notify customers of violations, but proactive inquiry can get you faster answers. You can also file a complaint with your state environmental agency.

Best Water Filters Based on Your EWG Results

Different contaminants require different filtration technologies. Match your priority contaminants to the right filter:

Frequently Asked Questions