America's water: a nationwide drinking water dataset

Drinking water data in the US is collected by 51 separate jurisdictions, in dozens of incompatible formats. WaterScore normalizes it into one comparable dataset: ~48,000 community water systems, ~200 contaminants, 1.35 million measurements. Here's what it shows.

Marissa Fichera·June 18, 2026·5 min

One dot per 25 water systems. Green sits under the federal limit; red is over it. The number at the right of each row is how many systems exceeded the limit. This chart shows the federally regulated contaminants, the subset of the ~200 with an enforceable national limit.

under the limitover the limitmedian
01 · WHAT'S IN THE WATER

value ÷ federal limit · log axis · 1 dot = 25 systems · sorted by number of systems with measured detections

Tested for but rarely detected

Byproducts with a health goal of zero

Of the nine disinfection byproducts the EPA regulates, three are flagged as probable carcinogens. These have a maximum contaminant level goal (MCLG) of zero, but no enforceable maximum contaminant level (MCL). But fear not - they are still regulated! These concentrations contribute to the TTHM and HAA5 group totals on the chart above.

Compliance is measured on those totals, so the national picture usually stops there. The individual species live in 50 separate state systems - here they are, nationwide, for the first time.

All three form whenever water is disinfected with chlorine - a side effect of making water safe to drink. A zero health goal doesn't mean any detection is dangerous; it means that for a probable carcinogen, the science won't name a threshold below which there is a certain nonexistent risk.

02 · WHAT WE CAN SEE

How accessible is your state's drinking water quality data?

Assembling a nationwide dataset means pulling from 51 separate jurisdictions (50 states plus Puerto Rico), each publishing in its own format and through its own channel. Some make the data far easier to obtain than others. Here is how they rank.

The largest state in the country sits in the easiest tier, and one of the wealthiest sits in the hardest. What separates them is mundane and entirely a choice: whether someone, at some point, built a public way in and kept it running.

A
Open APIQuery and go. The data feed is programmatically accessible, so a builder can pull every system’s records directly.
B
Bulk exportA downloadable file of the whole dataset. Harder than an API only because you export and process it yourself.
C
Centralized portalOne public portal where each system’s data can be looked up, system by system. No single feed or file, but everything lives in one place.
D+
Templated PDFsNo data feed, just documents, but at least they are uniform. The state posts every system’s annual water quality report as a PDF, all following the same template, in one place. Because the format is consistent, the numbers can be extracted in bulk without AI.
D−
Non-uniform PDFsDocuments, but every one is different. The data lives only in published reports, and the reports do not share a format. Layouts, tables, and labels vary from system to system, so pulling the numbers reliably requires AI extraction rather than a simple parser.
F
No accessible, centralized sourceNo API, no bulk file, no portal, no document repository you can work with. Getting the data means filing a formal records request or contacting a person at the agency.

Did we get something wrong? Let us know.

WaterScore aggregates publicly reported drinking water data from the state and territorial agencies responsible for administering the Safe Drinking Water Act, along with the U.S. Environmental Protection Agency. Every grade, contaminant level, and water system record on this site traces back to data these agencies make public. We are grateful for their work collecting and reporting it.

Data sources by state and territory:

  • Alabama: Alabama Department of Environmental Management
  • Alaska: Alaska Department of Environmental Conservation
  • Arizona: Arizona Department of Environmental Quality
  • Arkansas: Arkansas Department of Health
  • California: California State Water Resources Control Board, Division of Drinking Water
  • Colorado: Colorado Department of Public Health and Environment
  • Connecticut: Connecticut Department of Public Health
  • Delaware: Delaware Division of Public Health
  • Florida: Florida Department of Environmental Protection
  • Georgia: Georgia Environmental Protection Division
  • Hawaii: Hawaii Department of Health, Safe Drinking Water Branch
  • Idaho: Idaho Department of Environmental Quality
  • Illinois: Illinois Environmental Protection Agency
  • Indiana: Indiana Department of Environmental Management
  • Iowa: Iowa Department of Natural Resources
  • Kansas: Kansas Department of Health and Environment
  • Kentucky: Kentucky Division of Water
  • Louisiana: Louisiana Department of Health
  • Maine: Maine Drinking Water Program, Maine Center for Disease Control and Prevention
  • Maryland: Maryland Department of the Environment
  • Massachusetts: Massachusetts Department of Environmental Protection
  • Michigan: Michigan Department of Environment, Great Lakes, and Energy
  • Minnesota: Minnesota Department of Health
  • Mississippi: Mississippi State Department of Health
  • Missouri: Missouri Department of Natural Resources
  • Montana: Montana Department of Environmental Quality
  • Nebraska: Nebraska Department of Water, Energy, and Environment
  • Nevada: Nevada Division of Environmental Protection
  • New Hampshire: New Hampshire Department of Environmental Services
  • New Jersey: New Jersey Department of Environmental Protection
  • New Mexico: New Mexico Environment Department
  • New York: New York State Department of Health
  • North Carolina: North Carolina Department of Environmental Quality
  • North Dakota: North Dakota Department of Environmental Quality
  • Ohio: Ohio Environmental Protection Agency
  • Oklahoma: Oklahoma Department of Environmental Quality
  • Oregon: Oregon Health Authority, Drinking Water Services
  • Pennsylvania: Pennsylvania Department of Environmental Protection
  • Rhode Island: Rhode Island Department of Health
  • South Carolina: South Carolina Department of Environmental Services
  • South Dakota: South Dakota Department of Agriculture and Natural Resources
  • Tennessee: Tennessee Department of Environment and Conservation
  • Texas: Texas Commission on Environmental Quality
  • Utah: Utah Division of Drinking Water
  • Vermont: Vermont Department of Environmental Conservation
  • Virginia: Virginia Department of Health, Office of Drinking Water
  • Washington: Washington State Department of Health
  • West Virginia: West Virginia Bureau for Public Health
  • Wisconsin: Wisconsin Department of Natural Resources
  • Wyoming: Wyoming Department of Environmental Quality
  • Puerto Rico: Puerto Rico Aqueduct and Sewer Authority

WaterScore · know-your-water.com