What’s in Washington D.C.’s drinking water?

Over 600,000 people are served drinking water by Washington D.C. Water and Sewer Authority, or D.C. Water, making it one of the largest water utilities in the U.S. With the release of the 2025 update to EWG’s Tap Water Database, we took a closer look at this expansive system serving the nation’s capital and compared it to the nation as a whole.

In addition to information about the drinking water quality in Washington, D.C., the Tap Water Database provides details about chemical and radioactive contaminants in the water of nearly 50,000 community systems nationwide.

The database also evaluates how these contaminant levels compare to federal legal limits and EWG’s own health-based standards for protection against harms such as a greater risk of cancer.

D.C.’s water comes from the nearby Potomac River via the Washington Aqueduct, which is owned and operated by the Army Corps of Engineers. The water is treated before it reaches residents.

Test results through 2024 showed 37 contaminants were in D.C.’s water, with 13 at levels above EWG’s health-based limits.

Key contaminants in Washington, D.C., tap water

Nitrate

The fertilizer chemical nitrate is found in D.C.’s water at levels 14 times EWG’s health guideline. Studies in the U.S. and other countries have found greater incidence of colorectal, ovarian, thyroid, kidney and bladder cancer among people exposed to nitrate in drinking water. 

Although nitrate contamination is often associated with rural areas, EWG analyses have found that urban water systems can also be affected, because of upstream agricultural pollution, storm water runoff and municipal wastewater discharges into waterways.  

A 2019 peer-reviewed study by EWG estimated that nitrate pollution in U.S. drinking water may be responsible for up to 12,594 cases of cancer a year, at a cost of up to $1.5 billion for health care.

Hexavalent chromium

Hexavalent chromium, or chromium-6, was detected in D.C.’s water four times higher than EWG’s health guideline. A 2008 National Toxicology Program study linked chromium-6 in drinking water to cancer in laboratory animals, and a 2015 study by researchers in California found an increased risk of stomach cancer in workers exposed to the contaminant.

EWG has long raised the alarm about chromium-6, releasing a landmark analysis and map of contamination across the U.S. in 2016. EWG maintains the interactive map, which charts contamination utility by utility.

Radium

D.C.’s water contains radium at levels almost eight times higher than EWG’s health guideline. Radium is a radioactive element that often occurs naturally in rocks and soil, and it is linked to bone cancer and other cancers. 

Lead

According to EWG’s analysis of 2023 tap water testing results, 90 percent of tested households had lead concentrations below 15 parts per billion, which is the federal lead action level. Results from only three of the 213 tests exceeded the action level.

Lead is a potent neurotoxin that impairs children’s intellectual development and alters their behavior and ability to concentrate. There is a strong scientific agreement that any amount of lead exposure during childhood is harmful and irreversible. 

Lead pipes, common in water lines installed before the 1930s, remain a key indicator of potential lead contamination in urban areas.  

If you live in D.C. and would like to find out more about lead in your tap water, contact D.C. Water and ask for a free test kit.

Disinfection byproducts

The D.C. Water and Sewer Authority utility page in the Tap Water Database shows that nine of the 13 contaminants exceeding EWG’s health guidelines are disinfection byproducts, an umbrella term that includes bromochloroacetic acid, bromodichloromethane, chloroform, dibromochloromethane, dichloroacetic acid, the haloacetic acids HAA5 and HAA9, total trihalomethanes and trichloroacetic acid. 

Drinking water must be disinfected to kill disease-causing pathogens, and this treatment process is one of the greatest accomplishments in public health. But it can produce toxic byproducts if the water contains organic matter such as soil, fertilizer and animal waste – all of which are likely present in D.C.’s untreated water.

Scientists have identified more than 600 disinfection byproducts in treated drinking water. Some of the most common are linked to DNA damage, cancer and other harms. In a 2020 study, researchers in Sweden found that pregnant women exposed to low levels of chlorinated drinking water byproducts  were more likely to give birth to underweight babies. 

Water filtration

EWG’s Tap Water Database can help you find the right water filter for your needs. On the utility’s page in the database, you can see what contaminants were found in your system that could be addressed by a particular type of filter.

Most of the contaminants in the D.C. system that exceed EWG’s health guideline will be reduced effectively by a simple countertop carbon filter. 

The exceptions are arsenic, chromium-6, nitrate and radium. Results of recent EWG tests of home filters found some pitcher filters can reduce levels of these contamination.

An advanced filter such as reverse osmosis is the most effective way to remove contaminants from drinking water – but this can cost more upfront than a typical carbon filter. 

If you’re in the market for a countertop carbon filter, make sure to check out EWG’s guide to countertop water filters.

Stay in the know

EWG’s Tap Water Database is a helpful tool, even if you’re not a Washingtonian. The database puts your tap water’s contamination into perspective. Once you find your utility in the database, the info about the local water quality can help you understand what’s in it. Then you can make informed decisions about how best to reduce your exposure to contaminants. 

In the weeks and months ahead, EWG will continue to produce original drinking water content, from scientific analyses to everyday solutions to eye-opening explainers. Stay in the know by subscribing to EWG’s email list and follow us on Facebook, Instagram and YouTube.