Sacramento, California – A new nationwide study led by Columbia University researchers has found that arsenic levels in public drinking water across parts of California may pose significant health risks, even when those levels fall below the current federal limit. The findings are renewing calls to lower the threshold for arsenic in drinking water and reassess what constitutes “safe” consumption — particularly for pregnant people and young children.
According to the study, public water systems in counties like Sacramento and Merced report arsenic concentrations as high as 11 micrograms per liter, surpassing the Environmental Protection Agency’s (EPA) current safety standard of 10 micrograms. But even water with arsenic levels at or below that legal limit was linked to troubling birth outcomes, including low birth weight, preterm delivery, and restricted fetal growth. The researchers also noted that long-term exposure to low levels of arsenic is associated with cardiovascular disease, type 2 diabetes, and elevated cancer risk.
Despite those findings, federal policy has yet to shift. An EPA spokesperson said that while the agency’s long-term goal is to reduce arsenic to zero, technical and economic constraints have made that goal unattainable. The current limit, the spokesperson said, reflects a balance between reducing health risk and ensuring water utilities can realistically comply.
California officials, however, acknowledge that the state’s drinking water regulations may no longer be sufficient in light of the new evidence. The California State Water Resources Control Board emphasized that the state already sets some of the most protective drinking water standards in the country, but agreed that the maximum contaminant level for arsenic “should be revised to a level that is more protective of human health, especially for infant development.”
Geology plays a central role in why California’s water systems are more susceptible to arsenic contamination. Much of the state relies on groundwater, which can absorb arsenic naturally occurring in local bedrock and sediment. In places like the Central Valley, arsenic-bearing minerals are deposited through erosion and released into aquifers over time. This geologic backdrop makes full elimination of arsenic particularly difficult, even with advanced water treatment.
While cities such as Sacramento report that their water systems remain below federal arsenic thresholds — with average concentrations around 2.3 micrograms per liter — other areas, particularly rural communities, continue to struggle. East Walnut Grove’s water reached 11 micrograms per liter in recent sampling, and privately supplied wells, which are unregulated, remain a largely invisible threat.
Experts warn that revising arsenic standards is a complex process requiring federal action, sustained investment, and long-term commitment. Still, they argue the evidence is clear: even low levels of arsenic can pose a serious risk.
“This study adds to a growing body of research suggesting that our current standards aren’t adequately protective,” said Dr. Peggy O’Day of UC Merced. “It’s time we treat arsenic exposure for what it is — not just a geological fact, but a public health issue.”
