How many drinking water contaminants are regulated?


There are more than 80,000 chemicals used in industry and commerce.

How many of them do you think are regulated in drinking water in the United States?

Only 96 out of 80,000! The majority of chemicals in drinking water are NOT regulated.

What has been done? What do the latest data show?

What about your own county? What can you do?


This website allows you to find out more about tap water quality in your home county, as well as the entire continental US.

We will look closer into 28 potentially most harmful chemicals, which are currently beyond government regulation.

Drinking water crises and regulations
Water Crisis Events
Water Legislation
What will you see here?

CLICK on the circle to explore the 28 chemical contaminants covered in this interactive website, and the label to learn more about these chemicals.

Let's look at the latest data.

The graph presents all the counties in the US. The y-axis is the Water contamination index*. Lower scores mean better quality. The x-axis is the number of water samples tested in a county. Higher numbers mean more extensive examination. The bubble size represents the population size of a county.

*Water contamination index = log base 10 of ratio between concentration and Method Reporting Limit (MRL).
e.g., chemical X is detected at 100 times the MRL, then its water contamination index is log_10(100)=2.

  • Summary score
  • Heavy metals
  • Highly fluorinated compounds
  • Synthetic organic contaminants
  • Volatile organic contaminants
  • Disinfection byproducts
  • Hormones
  • North East
  • Mid-Atlantic
  • South-East
  • Mid-West
  • South West
  • North West
  • West

Five counties with the highest contamination results in the USA
What's in your water?

The latest survey of unregulated contaminants in U.S. tap water is the EPA third Unregulated Contaminant Monitoring Rule. All public water supplies serving more than 10,000 people and 800 representative PWSs serving 10,000 or fewer people were monitored for 28 chemical contaminants from 6 groups during a 24-month period from January 2013 through December 2015. Explore the tap water contamination level by county or state by hovering over or clicking the region on the map.

  • Summary score
  • Heavy metals
  • Highly fluorinated compounds
  • Synthetic organic contaminants
  • Volatile organic contaminants
  • Disinfection byproducts
  • Hormones
What can you do to help?

There are a variety of ways you can help, from activism and “good” citizenship (e.g., organizing demonstrations, voting) to private-sphere behaviors.

lab testing icon Contaminated tap water may look fine, smell fine, and taste fine. The best way to figure out the water quality is to send it for testing. If you are interested in testing your tap water for the list of compounds shown on this website. Here is a list of labs certified by the Environmental Protection Agency.
activism icon Tap water is a public good and deserves a systematic fix. The best way to demonstrate your green citizenship is to let your voice be heard. This way you also help underprivileged groups who may not have the resources to reach out. You can reach out to local political officials and express your concern.
ngo icon Some NGOs in the US have realized this challenge the country faces and started to provide information to the public on tap water quality. Environmental Working Group has assembled over 30 million data entries from 50 states over the last decade and curated them in their tap water quality database.
ngo icon Skip that bottled water! Bottled water is NOT better quality and is usually BAD for the environment. An alternative quick-fix (though not perfect) is to use a water filter at home. There is no one size fits all; the best water filter will fit your own needs and the budget of your family. We have a guide for you.
Who We Are

Xindi (Cindy) Hu

Cindy is a data scientist at Mathematica. Her research interests include environmental health, predictive modeling, and data analytics to support health policy decision making.

Dan Tompkins

Daniel is a candidate for Masters in Design Studies (MDes-- Art, Design, and the Public Domain) at Harvard University. He received a Bachelor of Architecture from Cornell University and works in a variety of design media.

Paul von Chamier

Paul is a candidate for Masters in Public Administration in International Development at Harvard University. He specializes in data analysis and econometrics. His professional experience includes working at the World Bank and P&G eBusiness.