Regulating and treating multiple drinking water contaminants as groups, instead of the standard method of targeting one at a time, would significantly benefit public health.
Millions of Americans have drinking water contaminated with hexavalent chromium and arsenic or nitrate, or all three, a new EWG map shows.
Treating tap water for these and other pollutants at once could prevent up to 50,000 lifetime cancer cases in the U.S, a recent peer-reviewed EWG study finds. For example, ion exchange is a water treatment that can help reduce arsenic, nitrate and hexavalent chromium together at once. This in turn lowers the cancer exposure risk for people drinking that water across the board.
The development of federal drinking water rules currently relies on the same years-old approach of focusing on a single contaminant. But grouping contaminants would support water utilities’ investment in treatment technologies that can be enhanced to reduce multiple pollutants simultaneously.
The sheer scale of drinking water contamination with hexavalent chromium and either arsenic or nitrate or both suggests the need to focus on approaches for regulating and treating several substances at once.
Need for more funding
Treating tap water to prevent diseases should be a priority. But many drinking water systems face tight budgets. The best and most efficient use of funds would be to invest in treatment that tackles multiple pollutants.
While simultaneous removal of multiple contaminants could improve public health, practical challenges exist. Installing treatment can be highly effective but costly, which may put it out of reach for many smaller utilities.
That’s why the findings of EWG’s study and maps can help to amplify calls to significantly boost federal funding for drinking water infrastructure in the coming years.
Spending taxpayer dollars more wisely up front on smarter tap water treatment could result in significant cost savings long-term through cancer cases and related healthcare costs avoided, compared to business as usual, focusing on one contaminant at a time.
But securing the dollars needed to fund such treatment will require utilities, state officials and Congress to change their thinking. Highlighting the tens of thousands of cancer cases that could be avoided with this new approach may help drive that change.
Three tap water contaminants
Hexavalent chromium
Hexavalent chromium, or chromium-6, is the harmful drinking water contaminant made notorious by the movie “Erin Brockovich.” It’s linked to significant health harms. Even low levels in tap water can increase the risk of reproductive harm, liver damage and stomach cancer.
And it contaminates the water of over 260 million people served by 7,538 utilities, with particular hot spots in California and Arizona.
The Environmental Protection Agency has not set a legal limit on the amount of chromium-6 allowed in drinking water.
For many years the industries responsible for chromium-6 contamination delayed the EPA’s safety review. But now, as part of a legal settlement, the agency must decide by 2027 whether to set an enforceable national drinking water standard for the chemical.
EWG recommends a health limit of 0.02 parts per billion, or ppb, to protect against the chemical’s cancer-causing effects. California’s lengthy regulatory process led in 2024 to a state limit of 10 ppb. But that’s a level some scientists deem to be 500 times too high.
Arsenic
Arsenic often contaminates drinking water that’s also polluted with chromium-6. Arsenic is a heavy metal and potent carcinogen that has been detected in all 50 states, contaminating the water of 12,945 utilities serving a total of 134 million Americans.
The EPA’s drinking water limit for arsenic is 10 parts ppb, which was set in 2001 and based largely on the cost at the time of removing the heavy metal.
Scientists have long warned that the agency’s limit does not fully protect against the risk of arsenic-related cancer. To that end, EWG advocates a much stricter health guideline of 0.004 ppb, the same as defined by California’s Office of Environmental Health Hazard Assessment.
Nitrate
The fertilizer chemical nitrate can also affect drinking water contaminated with chromium-6 and arsenic. Nitrate has been detected in 49 states, affecting the tap water of 263 million Americans served by 26,644 systems. Excessive nitrate in water can increase the risk of cancer and birth defects and lead to oxygen deprivation in infants.
The EPA’s legal drinking water limit for nitrate, set in 1962, is 10 parts per million, or ppm. It doesn’t fully protect against cancer risk or harm to a developing fetus. EWG’s health guideline is just 0.14 ppm, which would reduce the cancer risk level to one in one million.
Existing federal regulations for nitrate and arsenic leave a lot of room for improvement. Reducing amounts of these contaminants below existing levels, even slightly, can have significant health benefits.
This approach would help lower the number of annual cancer cases in the U.S., by reducing the level of all the chemicals at once. In turn, this would cut the potential risk of cancer from exposure.
Another state-level map shows the theoretical cancer cases that could be avoided if chromium-6 and arsenic were reduced to the public health guidelines in systems where it’s been detected, with most estimated cases reduced in California and Arizona.
Map: Estimated cancer cases prevented by reducing chromium-6 and arsenic in affected water systems.
EWG’s peer-reviewed study, published in the journal Environmental Research, finds that drinking water treatment using a multi-contaminant approach, tackling several pollutants at once, could prevent more than 50,000 lifetime cancer cases in the U.S.
In the paper, EWG scientists analyzed more than a decade of data from over 17,000 community water systems.
By way of example, if water systems with chromium-6 contamination also reduced arsenic levels to between 27% and 42%, it could prevent up to four times the number of cancer cases that lowering chromium-6 levels alone would prevent, the study found.
In California, eight of 10 potential cancer cases linked to the presence of chromium-6, arsenic and nitrate are linked to arsenic exposure. Arizona, California and Texas bear the highest burden of arsenic pollution and would gain the most from multi-contaminant water treatment efforts.
Rethinking water treatment
EWG’s map and study show the potential significant health benefits of applying a co-contaminant approach to water treatment, even as the process of developing federal drinking water regulations mostly takes a narrow single contaminant approach.
These EPA rules usually evaluate the cost and benefit of water treatment on a one-contaminant basis, a model EWG’s report calls outdated and inefficient. Shifting to a multi-contaminant approach, such as adopting a treatment technique standard, would better address the challenges of emerging contaminants.
Water systems routinely comply with regulations for multiple contaminants. But it’s possible to improve treatment so it efficiently removes several at once. Contaminants that are similar to one another, as nitrate, arsenic and chromium-6 are, can all be reduced with ion exchange.
For example, the California city of Chino has installed technology to treat their groundwater to remove nitrate, chromium-6 and the rocket fuel component perchlorate at the same time. More data is needed to support practical applications in real-world scenarios.
But federal regulation of, and funding for, tap water infrastructure will require a wholesale shift in thinking to a system that prioritizes a multi-contaminant group approach to treatment. Such solutions could even be tailored to the needs – and resource limits – of communities.
California’s State Water Board has suggested some smaller water systems could use point-of-use treatment as an alternative to community level treatment for the smallest communities to keep costs down while also improving drinking water. Such approaches would likely use reverse osmosis technology and remove most contaminants in drinking water.
Strategies like these are necessary to overcome financial barriers to better drinking water regulations and treatment.
Beyond individual health, the benefits of clean water extend to increased productivity and well-being. Clean drinking water is fundamental to a thriving society, and greater attention to this forward-looking approach to treatment can help achieve that goal.
