Map Shows Tap Water For Nearly 100M People Has Toxic Chromium-6 Mixed With Arsenic And Nitrate

Tackling all three contaminants in water treatment could prevent up to 50,000 cancer cases

Thousands of communities have water utilities serving almost 100 million people drinking water polluted with hexavalent chromium, also called chromium-6, as well as arsenic and nitrate. That’s the finding of a new report and interactive map published today by the Environmental Working Group.

These contaminants are known to cause cancer and other health harms, and are toxic at extremely low levels. But most drinking water treatment systems only tackle one contaminant at a time.

Filtering several co-occurring contaminants together instead could prevent up to an estimated 50,000 cancer cases in a lifetime, according to a peer-reviewed paper by EWG scientists.

Need for updated treatments
“This is a significant national problem and public health issue,” said Tasha Stoiber, Ph.D, a senior scientist at EWG. “People are exposed to multiple contaminants in their drinking water, and analysis shows that regulating and treating them simultaneously is a more effective and efficient approach than focusing on each chemical separately.

“Updating treatment strategies could improve health while making better use of resources,” said Stoiber.

Most drinking water regulations focus on exposure to one chemical at a time. It is a slow, outdated approach that fails to reflect the real-world mixtures of chemicals Americans are exposed to every day. This approach also doesn’t accurately account for the benefits of removing multiple contaminants at the same time.

EWG’s new report and map contamination hot spots in Arizona, California and Texas, where tap water frequently contains chromium-6, arsenic and nitrate together at levels that pose significant long-term health risks. Yet the levels at these hot spots comply with existing federal drinking water standards.

Three cancer-causing chemicals in tap water
Chromium-6 is the harmful industrial drinking water contaminant made infamous by the movie “Erin Brockovich,” based on the true story of Pacific Gas & Electric’s poisoning of a small California community. Even low levels in tap water can increase the risk of reproductive harm, liver damage and stomach cancer.

It’s found in the water of over 260 million people served by 7,538 utilities nationwide, with particularly high levels in California and Arizona.

Arsenic, a toxic heavy metal and known carcinogen that occurs naturally in soil, often appears with chromium-6 in drinking water. It has been detected in all 50 states, contaminating the water of 12,945 utilities serving a total of 134 million Americans.

Long-term arsenic exposure increases the risk of several types of cancer, including bladder and lung cancer.

Nitrate contamination, which comes from nitrogen in agricultural fertilizer and manure, is also widespread, detected in 49 states, affecting the tap water of 263 million Americans served by 26,644 water systems. Nitrate in water can increase the risk of cancer and birth defects, and high levels can fatally deprive infants of oxygen.

Each of these cancer-causing contaminants can be removed through similar treatment, such as ion exchange or reverse osmosis, which suggests they could be removed all at once.

Yet most drinking water regulations in the U.S. are developed assuming a single pollutant – an approach that fails to account for the benefits provided by filtration technology that addresses co-occurring contaminants simultaneously.

California’s drinking water contamination challenges
Thousands of Californians rely on water that contains chromium-6, arsenic and nitrate, with arsenic driving eight out of 10 potential cancer cases from these contaminants.

EWG scientists recommend much stricter health guidelines than the state’s limit of 10 parts per billion, or ppb, for chromium-6 in water, set in 2024. EWG aligns with the public health goal for arsenic of 0.004 ppb, set by the state’s Office of Environmental Health Hazard Assessment.

"Millions of Californians are exposed to a toxic soup of cancer-causing chemicals in their tap water every day, yet state policy continues to move too slowly to address weak limits and maximize public health protections,” said Bernadette Del Chiaro, EWG’s senior vice president for California.

“California has a reputation for innovation. This is an opportunity to lead the nation in protecting public health by modernizing water treatment and setting new standards for clean, safe water,” she said.

Some California communities are already taking action, upgrading treatment to efficiently remove several emerging contaminants. For example, Chino has installed technology that treats their groundwater to simultaneously remove nitrate, chromium-6 and the rocket fuel component perchlorate.

A call for bold federal action
EWG's report and map point to a major flaw in rules used by the Environmental Protection Agency that require water systems to evaluate the cost and benefit of water treatment on a one-contaminant basis. This approach ignores the way chemicals appear in mixtures and can be removed from water together by a single filtration system.

“The public health benefits are undeniable, but the EPA is moving too slowly to protect Americans from these hazardous chemicals in drinking water,” said Melanie Benesh, EWG’s vice president of government affairs. “Our laws haven’t kept pace with the risks from our tap.”

“It’s time for Congress and federal regulators to adopt a 21st-century strategy for a 21st-century crisis. Investing in water treatment not only prevents cancer, it improves the health for millions. Yet political will, not science or cost, is the barrier,” said Benesh.

“Cutting the EPA’s budget now only makes the problem worse. We should not be shrinking the agency charged with keeping our tap water safe but instead making sure every dollar spent goes further in protecting public health like filtering out multiple contaminants at a time,” she added.

Turning data into action
EWG scientists stress that the benefits of clean water extend beyond individual health. Investing in smarter water treatment can lead to stronger communities, increased productivity and improved quality of life. With the data and map now in hand, the question is no longer whether we can fix our broken drinking water system, but whether there is the political will to do so.

“The challenges are well known and the solutions are within reach,” said Stoiber. “What we need now is action – smarter rules, stronger funding and a real commitment to provide clean water to every community. EWG’s new map makes the problem visible. But visibility isn’t enough.

“Clean drinking water is essential to health and embracing modern treatment approaches can help make that a reality,” Stoiber said.

About The Environmental Working Group (EWG)
The Environmental Working Group (EWG) is a nonprofit, non-partisan organization that empowers people to live healthier lives in a healthier environment. Through research, advocacy and unique education tools, EWG drives consumer choice and civic action.