California’s drinking water has elevated levels of a certain contaminant found to be associated with adverse birth outcomes, causing experts to advise that safe water advisories need to be updated.
According to a nationwide study led by researchers at Columbia University, parts of the state have levels of arsenic in public drinking water higher than 5 micrograms per liter.
While the Environmental Protection Agency (EPA) currently maintains that levels of arsenic in drinking water are safe at 10 micrograms per liter or less, the study found certain health risks were associated with lower levels.
Researchers found that consumption of drinking water with levels of arsenic of 10 micrograms or less were connected to a higher chance of babies being born preterm, with lower birth weights, or smaller than expected for their gestational age.
Other research has found that cardiovascular disease and type 2 diabetes have been linked to low levels arsenic exposure, while chronic exposure to the mineral has been associated with heightened cancer risks.
Navigating Water Quality Standards
An EPA spokesperson previously told Newsweek that the maximum contaminant level for arsenic in drinking water was based on an assessment of implementation and cost, as well as public health.
While the goal is for the level of arsenic to be zero, because of “technical limitations” and cost, the goal cannot be met by water systems, the EPA said.
Therefore, the EPA’s current maximum contaminant level is based on a “health risk reduction and cost analysis,” ensuring public health has been considered, while giving water service bodies a more feasible target.
“California has some of the safest water in the nation, with 25 maximum contaminant levels that are set at more protective health levels than the federal levels, and 14 maximum contaminant levels for contaminants that have no federal equivalent,” the California State Water Resources Control Board told Newsweek.
“This new study makes clear what California already understood—that maximum contaminant level should be revised to a level that is more protective of human health, especially for infant development. The state has been working to address this,” the board added.
Sacramento County was one of the regions with higher levels of arsenic in public drinking water and the City of Sacramento Department of Utilities told Newsweek that it “closely monitors water quality and is committed to meeting or exceeding all state and federal drinking water standards, including those for arsenic.”
In the city’s most recent Consumer Confidence Report, arsenic levels in the drinking water system were below the EPA’s maximum contaminant level, at an average of 2.3 micrograms per liter, while its groundwater levels ranged from non-detectable to 4.7 micrograms per liter.
“The City of Sacramento’s drinking water meets or exceeds all federal and California state water quality standards,” the city’s Department of Utilities told Newsweek.
It added that it “supports California’s existing and established science-based approach to setting or modifying drinking water quality standards.”
Meanwhile, Sacramento County Water Agency told Newsweek: “We are in compliance with the state’s standards. We do not dictate the guidelines.”
According to the agency’s 2024 Consumer Confidence Report, Northgate and Southwest Tract had ranges of arsenic in water that reached 5 micrograms per liter, while East Walnut Grove had levels that reached higher than the EPA guidance—at a range of non-detectable to 11 micrograms per liter.
Merced County was another area of the state that appeared to have higher levels of arsenic in drinking water, per the study’s map.
A public information officer for the city of Merced told Newsweek that the city’s drinking water is “routinely tested and remains in compliance with all state and federal safety standards, including those for arsenic.”
“We monitor over 250 contaminants and collect thousands of samples annually to ensure water quality,” they added. “While we can’t comment on conditions outside city limits, we take emerging health research seriously and remain committed to providing safe, clean water to our residents.”
When approached for comment, the California Department of Public Health pointed Newsweek to the state’s Water Resources Control Board.
Why Does California Have Higher Levels of Arsenic?
As arsenic is a natural element that can be found in soils, sediments and groundwater, it can feed into public drinking water systems, but some areas will have higher levels because of natural geology, certain human activities, irrigation practices and other factors.
Many community water systems in California “draw upon groundwater that is naturally elevated in arsenic, so it’s not unusual—even with treatment or mixing of waters—that detectable arsenic remains once water is supplied to users,” Bethany O’Shea, a professor in the environmental and ocean sciences department at the University of San Diego, told Newsweek.
The reason California’s groundwater is higher in arsenic is a result of “geologic sources,” Janet Hering, former director of the Swiss Federal Institute of Aquatic Science and Technology, told Newsweek.
Although, for the city of Los Angeles, water supply is affected by “inputs of geothermal water at Hot Creek in Owens Valley,” she added.
In the Central Valley, arsenic originates in certain minerals in rocks of the Sierra Nevada foothills, Peggy A. O’Day, a professor in the Department of Life and Environmental Sciences at University of California, Merced, told Newsweek.
“Weathering and erosion of these rocks transported arsenic-bearing minerals to the Central Valley where they were deposited as sediments and buried mineral alteration and dissolution can eventually release arsenic into groundwater,” she said.
Although, while the study specifically looks at public water systems, O’Shea warned that arsenic can be found in privately supplied water from wells.
“An abundance of research exists showing elevated arsenic in wells across states like Maine, New Hampshire and Vermont,” she said.
She added that, as a result, “similar birth outcome risks may exist for people drinking from private wells containing arsenic.”
“This underscores the need for more research to better understand how even small concentrations of arsenic in all types of drinking water, public or private, might lead to health risks such as adverse birth outcomes,” O’Shea said.
What Should Be Done?
Experts who spoke with Newsweek believed that the current maximum contaminant level for arsenic should be lowered in light of the findings of Columbia University’s study but added that this might not be as simple as it sounds.
“The important finding of this study is that even those small concentrations of arsenic remaining may be harmful, suggesting that a lower water standard may be effective,” O’Shea said.
A number of countries, like Denmark, and some U.S. states, such as New Jersey and New Hampshire, have set water standards at 5 micrograms per liter, lower than the 10 microgram per liter level set by the EPA.
“Setting that goal of zero as a standard—or even lowering the standard by half, to 5 micrograms per liter—may help alleviate health risks,” O’Shea said.
O’Day said the study supports a “history of evidence” indicating that the current level for arsenic “may not provide a sufficient level of protection from adverse health impacts for all segments of the population.”
“Federal drinking water standards should be reviewed and updated based on new, reliable scientific information,” she said.
Although O’Day added that lowering the maximum contaminant level for any contaminant is “a long process and does not necessarily ensure that public water suppliers have the resources to meet it without an undue cost burden on their customers.”
Ultimately, “more funding needs to be directed towards rural and underserved communities to improve their infrastructure and testing to provide safe drinking water that meets health-based standards for arsenic, lead and other contaminants,” she said.
Hering also cautioned that “legally, lowering the [maximum contaminant level] has to reflect practical considerations and economic feasibility.”
“Personally, I think it makes sense to try to prioritize potential adverse exposures and consider other possible contaminants as well as arsenic,” she said.
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