More than 100 million Americans are drinking water contaminated with a cocktail of harmful chemicals, according to a new report.

The Environmental Working Group (EWG), an advocacy group focused on toxic chemical investigation, examined data regarding contaminants in over 17,700 community and groundwater systems across America.

The EWG discovered that nearly 50% of the US population is exposed to water contaminated with chromium-6, nitrate, and/or arsenic, all of which are known or suspected carcinogens.

These toxins have been detected in the drinking water of 82% of Americans (263 million are affected by nitrate, 260 million by chromium-6, and 134 million by arsenic), with a concerning number of households receiving water containing all three contaminants.

The latter was a key finding from the study, with the pollutant combination tainting water that flows to roughly 100million Americans.

The EWG researchers estimated the number of lifetime cancer cases that would be expected to arise in each water system area. 

Arsenic, a toxic heavy metal that seeps into groundwater from natural deposits, is a powerful carcinogen linked to cancers of the bladder, lungs, and skin.

Nitrate, a chemical mainly from agricultural fertilizer runoff, contaminates both groundwater and surface water. It is associated with colorectal cancer and thyroid issues and poses a serious risk of causing ‘blue baby syndrome’ due to oxygen deprivation in infants.

Hexavalent chromium, also known as chromium-6, is a toxic chemical central to the well-known 1996 California lawsuit by Erin Brockovich. This case connected the contaminant to cases of cancer among people who consumed polluted water. It is an industrial contaminant linked to cancers of the lung, stomach, and liver, even at low exposure levels.

Dr Tasha Stoiber, a senior scientist at EWG and lead author of the study, said: ‘Drinking water is contaminated mostly in mixtures, but our regulatory system still acts like they appear one at a time.

‘This research shows that treating multiple contaminants together could prevent tens of thousands of cancer cases.’

For this study, the researchers at EWG combined national testing data from the Environmental Protection Agency (EPA) with state-level records spanning 2011 to 2023. 

They then calculated the cancer risk associated with these chemicals using safety levels established by California’s Office of Environmental Health Hazard Assessment (OEHHA), which are hundreds of times stricter than federal limits.

The OEHHA set the maximum safety levels for arsenic at 0.004 micrograms per liter, chromium-6 at 0.02 micrograms per liter and nitrate at 0.14 milligrams (equivalent to 140 micrograms) per liter. 

In their final findings, the EWG used parts per million (ppm) and parts per billion (ppb) to denote concentrations in water. 

The EPA has set a maximum safety limit for arsenic in water at 10 ppb, while the limit for nitrate is 10 ppm. The federal government does not have a universal safety limit for chromium-6. 

According to the National Research Council of the National Academy of Sciences, the cancer risk associated with the EPA’s arsenic standard is unusually high. 

Drinking water at the legal arsenic limit of 10 ppb poses a 1 in 300 lifetime cancer risk, according to the study.

The research also found that the federal limit for nitrate (10 milligrams per liter) is potentially insufficient for protecting against stomach cancer.

After analyzing 60 relevant studies, researchers from the UK and Norway found a significant association between the toxin and the disease: For every nitrate concentration increase of 10 milligrams per liter, the risk of stomach cancer nearly doubled. 

Health experts affirm there is no safe threshold for chromium-6 in drinking water. 

The California public health goal of 0.02 ppb is not a ‘safe’ level, but rather the concentration estimated to pose only a one-in-a-million cancer risk, the EWG said. 

But how do these toxins end up in our water? 

Arsenic is largely a problem of natural geology, while chromium-6 and nitrate are more closely tied to human activity.

States out West, where water tends to be contaminated with all three toxins, have geology rich in arsenic-containing minerals. The region’s arid conditions mean communities rely more on groundwater, which has had more contact with these arsenic-rich rocks over time.

While the West Coast’s water systems are primarily plagued by multi-substance contamination, states in the Southeast – including Kentucky, Tennessee, Alabama and Georgia – see more contamination with chromium-6 and nitrate. 

The Southeast, where drinking water contains unsafe levels of nitrate and chromium-6, sees a disproportionately high burden of cancer. States with lower concentrations of contaminants and fewer affected water systems tend to have lower cancer rates compared to the national average

Chromium-6 is primarily an industrial pollutant. The Southeast, where chromium-6 and nitrate contamination commonly appear, has a long history of industries that used chromium: metal plating, textile manufacturing and cooling tower construction. 

On the other hand, nitrates from fertilizers seep into groundwater through the soil. This is a significant problem in any area with intense crop farming, large-scale animal feedlots or even areas with a high number of golf courses.

This same region of the country sees the highest burden of cancers compared to the rest of the nation, with incidences ranging from 472 cases of cancer for 100,000 people in Georgia to 476 cases per 100,000 people in Arkansas.

The national average, for comparison, is 449 cases per 100,000 people.

Several major cities are located in regions with geology that naturally contains arsenic or chromium-6. 

Houston, Miami, Albuquerque, Phoenix, and Las Vegas all had water contaminated by all three toxins, while North Carolina’s water systems showed contamination by chromium-6 alone.

Water serving homes in New York City, Chicago, Atlanta, Nashville and Seattle is primarily contaminated with chromium-6 and nitrate, but not arsenic. 

Generally, rural states with plenty of remote areas saw far fewer contaminated water systems. 

Arsenic, nitrate and chromium-6 are widespread tap water contaminants. Arsenic and chromium-6 are potent carcinogens linked to various cancers, while nitrate poses a severe risk of ‘blue baby syndrome’ and is also associated with cancer (stock)

With the exception of Omaha and a string of smaller towns tracing Highway 30 going west, Nebraska overall appeared relatively free of such contaminants. 

Similarly, in the eight Wyoming cities whose water systems contained chromium-6 and/or nitrate, only one, Gillette, had all three. 

States with lower concentrations of contaminants and fewer affected water systems tend to have lower cancer rates compared to the national average.  

Wyoming’s rate, for instance, is 407 cases per 100,000 people, while Utah’s is about 422 cases per 100,000 people. 

The EWG said that regulating groups of toxic chemicals in tap water, rather than one at a time, could prevent more than 50,000 cancer cases in the US. 

For example, if a new water treatment standard for chromium-6 were set at five parts per billion and systems also reduced co-occurring arsenic levels by just 28 percent, it could prevent an estimated 2,647 lifetime cancer cases, doubling the benefit of targeting chromium-6 alone.

Adopting this strategy would maximize health benefits and could be more cost-effective for water utilities and the communities they serve.

Water utilities are legally responsible for treatment, but the financial burden is shared between residents (through higher bills) and taxpayers (through government assistance programs).

Sydney Evans, senior EWG scientist and co-author of the study, said: ‘Ensuring clean drinking water for all communities is about fairness and equity.

‘Communities in the US that rely on groundwater are often affected by these contaminants. New water treatment technologies offer a chance to improve water quality overall. This strengthens the case for action and investment.’

By addressing multiple contaminants with shared treatment solutions, utilities could potentially reduce long-term capital and operational costs compared to installing separate systems for each chemical. 

‘Beyond individual health, the benefits of clean water extend to increased productivity and well-being,’ the EWG said.

‘Clean drinking water is fundamental to a thriving society, and greater attention to this forward-looking approach to treatment can help achieve that goal.’