Every day, millions of Americans turn on their faucets and fill glasses with tap water, trusting that what flows from the spout is clean, safe, and healthful. Water is, after all, fundamental to life. It composes more than half the human body, and no living organism can survive without it. From hydration and nutrient transport to temperature regulation and detoxification, water plays an essential role in virtually every function of the human body. So it is only natural that we would place tremendous trust in the quality and safety of our drinking water. But what if that trust has been misplaced?

Across the United States, tap water often carries with it a hidden cocktail of contaminants. Though these chemicals are often present in concentrations that comply with federal safety standards, recent research suggests that these standards may be dangerously outdated. For decades, regulatory frameworks have addressed contaminants one by one, a process that is both slow and ill-suited to keeping up with the rapidly evolving landscape of chemical exposure. Meanwhile, new contaminants are discovered regularly, and the long-term health impacts of their combinations remain largely unknown.

Organizations like the Environmental Working Group (EWG) have taken up the mantle of uncovering the truths about the quality of America’s drinking water. Through pioneering research and relentless advocacy, they are shedding light on a harsh reality: even when water meets the current federal legal limits, it may still pose significant risks to public health. Their findings are stark, and they demand a reckoning with the assumptions that have shaped water safety regulations for decades.

One of EWG’s most influential contributions to public knowledge is their Tap Water Database. It is a sweeping repository of over 32 million water quality test results from more than 50,000 community water systems across the country. The data paints a troubling picture. Contaminants such as arsenic, radioactive elements like uranium and radium, disinfection byproducts, and nitrate are found in tap water systems serving communities both large and small. While these substances may be individually regulated, their combined effects are often ignored, and science has yet to fully understand the risks posed by these chemical mixtures.

Consider the state of California, where a case study applied EWG’s novel cumulative risk framework to existing water data. Although the water generally met federal safety standards, researchers identified over 20 carcinogens present at levels significant enough to increase the risk of cancer. Their estimates attributed more than 15,000 lifetime cancer cases to drinking water exposure alone. This analysis, published in the journal Environmental Health in 2019, was the first of its kind and challenged the deeply rooted notion that compliance with federal regulations equates to safety.

EWG extended this research to a national scale and found an even more unsettling figure: more than 100,000 additional cancer cases across the United States could be linked to contaminants in tap water. The primary culprits? Arsenic, disinfection byproducts, and radioactive contaminants, especially in communities served by smaller water systems that often rely on untreated or minimally treated groundwater. These smaller systems, due to their limited resources and infrastructure, frequently face higher exposure levels, making them especially vulnerable.

The role of disinfection by products is particularly paradoxical. Chlorine and similar agents are necessary to eliminate bacteria and viruses in water. Without them, communities would be at risk of devastating waterborne diseases. However, when these disinfectants react with organic matter in the water—such as plant debris and sediments—they form toxic byproducts. These compounds, found in the drinking water of most Americans, have been linked to cancer and other health issues, turning a protective measure into a potential hazard.

In 2020, the EWG expanded its testing to include previously unregulated haloacetic acids, a class of disinfection byproducts that had not been thoroughly studied. The results revealed a widespread presence of these chemicals and raised new alarms about the health risks they pose. The data emphasized a critical flaw in how drinking water standards are established: many guidelines are based on outdated science, and they fail to account for real-world exposures to multiple contaminants. To truly safeguard public health, the process must incorporate findings from human studies and reflect the full spectrum of pollutants found in today’s water systems.

Another area of concern is nitrate, a contaminant primarily associated with agricultural runoff. The EPA’s current legal limit for nitrate is aimed at preventing methemoglobinemia, or “blue baby syndrome,” a potentially fatal condition in infants. Yet new research shows that nitrate exposure can also elevate the risk of cancer and harm fetal development. EWG’s 2019 analysis estimated that nitrate pollution in drinking water could be responsible for nearly 12,600 excess cancer cases per year and more than $1.5 billion in health care costs. It may also contribute to thousands of cases of very low birth weight and preterm births annually.

The recommended nitrate limit proposed by EWG is almost 100 times stricter than the EPA’s current standard. This discrepancy underscores the urgent need for updated, health-based guidelines that reflect contemporary scientific understanding. The current federal thresholds, shaped more by political compromise than public health science, are no longer sufficient to protect a nation facing new and mounting environmental challenges.

The broader implication of EWG’s research is that our approach to regulating water safety must evolve. It is no longer enough to assess one chemical at a time, ignoring the synergistic effects that occur when multiple pollutants are present. Instead, we must develop comprehensive frameworks that evaluate the cumulative impact of contaminants. This approach would not only provide a more accurate picture of risk but also better inform decisions about where to invest in water infrastructure and treatment technologies.

Communities served by smaller water systems, particularly those in rural or underserved areas, often face the greatest risks. These systems struggle with limited funding and outdated infrastructure, which hampers their ability to address contamination effectively. Investments aimed at improving water quality must prioritize flexibility and scalability to ensure that even the smallest communities receive the protection they deserve. The stakes are too high to continue leaving these areas behind.

Federal agencies like the EPA are responsible for setting the standards that determine whether drinking water is safe. But as EWG’s findings demonstrate, many of these standards fail to account for the true risks posed by modern-day water contaminants. While a glass of water from the tap may appear clean, its invisible contents could harbor substances that slowly erode health over time. For the average person, the realization that their water may not be as pure as it seems is deeply unsettling. Yet awareness is the first step toward change.

The solution requires a collective effort. Scientists must continue to conduct rigorous research to understand the health impacts of contaminant mixtures. Policymakers must be willing to update outdated regulations and adopt health-protective standards informed by the latest evidence. Communities must be empowered with transparent information about their water supply, and consumers must demand accountability from both industry and government. Change is possible, but it begins with a fundamental shift in how we think about water safety. Drinking water is not just a basic necessity; it is a cornerstone of public health. When the integrity of that foundation is compromised, the consequences ripple through every facet of life. It is time to treat water quality with the seriousness it deserves, to recognize that what we do not see can still harm us, and to work toward a future where every sip from the tap is not only refreshing, but truly safe. That future depends on new frameworks, renewed commitment, and the recognition that the health of our water is inseparable from the health of our people.