A new Yale School of the Environment study finds that while Jackson, Mississippi’s tap water met federal safety standards, corrosion risks, aging plumbing, and social inequality put vulnerable residents at greater risk than systemwide data indicated.
When the water system in Jackson, Mississippi, failed in 2022, more than 150,000 residents were left without reliable access to safe drinking water. For months — and in some cases years — boilwater notices became part of daily life. While the crisis drew national attention to broken pumps and aging pipes, a new study led by researchers at the Yale School of the Environment found that even when water samples met primary federal drinking water standards they often did not meet secondary standards.
The research, published in Water, provides a detailed look at what was actually coming out of people’s taps in the wake of the crisis. By combining water sampling with demographic data and spatial analysis, the team examined not only whether water met federal safety standards, but also how exposure risks varied across neighborhoods and among vulnerable residents.
“This research can help residents better understand water contamination and alert the government and water companies to potential hazards that should be addressed to avert another crisis,” said study co-author Dorceta Taylor ’85 MFS, ’91 PhD, the Wangari Maathai Professor of Environmental Sociology at YSE.
Researchers collected and analyzed tap water samples from homes and businesses across the Jackson metropolitan area, focusing on locations with young children, older adults, or other vulnerable populations. Using the U.S. Environmental Protection Agency’s updated Lead and Copper Rule sampling protocol, they tested for metals, disinfectant-related chemicals, and corrosion indicators.
While all samples met federal primary drinking water standards for contaminants, such as lead and copper, every site exceeded secondary standards, which are linked to taste, odor, discoloration, and, critically, corrosion in pipes. Seven locations also showed chlorine-to-sulfate mass ratios high enough to signal elevated corrosion potential — a condition that can increase the likelihood that metals will leach from plumbing over time.
This research can help residents better understand water contamination and alert the government and water companies to potential hazards that should be addressed to avert another crisis.”
That distinction is key, the researchers say, because regulatory compliance does not necessarily mean risk-free water.
“Our findings highlight a key limitation: Water can comply with federal standards while still posing localized corrosion risk,” said lead author and doctoral student Ambria McDonald. “Our study suggests that regulatory monitoring is most effective as a system-level indicator, but it should be complemented with more targeted monitoring or corrosion control assessments at the household level, particularly in communities with older infrastructure and vulnerable populations.”
The study also found that the highest lead levels appeared in first-draw samples — water that had been sitting in pipes for several hours — while concentrations dropped after the tap was flushed. That pattern suggests that lead exposure is more closely tied to conditions inside homes and buildings than to uniform contamination across the distribution system, underscoring the importance of sampling methods that capture real-world exposure, particularly in older housing stock.
“Risks are not evenly distributed across a water system,” McDonald said. “Instead, they tend to cluster in homes with older plumbing materials or service lines, which means that vulnerable populations may experience higher exposure than system averages would suggest."
For years, Jackson residents were instructed to boil their water to reduce microbial contamination. Yet, boiling does not remove metals — and can sometimes concentrate them.
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The research team tested water both before and after boiling and found that although lead levels remained below federal action thresholds, the process did not eliminate the risk of metal exposure. The result highlights a public health dilemma: The standard emergency guidance for unsafe water may not address all forms of contamination.
Rather than presenting Jackson as a singular disaster, the researchers say that the findings could be viewed as a warning to other U.S. cities with aging infrastructure and limited financial capacity. More than 300 million Americans rely on community water systems, many of which face similar pressures from deferred maintenance, workforce shortages, and climate-related stress.
The authors say that improving corrosion control, optimizing treatment processes, and expanding long-term monitoring — especially in historically marginalized communities — are essential next steps.
“While Jackson represents a high-profile case, the broader message is that proactive monitoring, corrosion control, and infrastructure investment are essential nationwide,” McDonald said. “Addressing these issues before they escalate into crises can help protect vulnerable populations and improve the long-term resilience of drinking water systems.”
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