• Tap water often contains harmful contaminants including PFAS, arsenic, nitrates, lead, and trihalomethanes at levels far above what health experts consider safe.

• Dozens of new contaminants are identified each year, yet many remain unregulated or poorly regulated.

• EPA legal limits are frequently outdated and can be far higher than modern health guidelines recommended by organizations like the Environmental Working Group (EWG).

• Certain contaminants pose serious health risks like cancer, endocrine disruption, developmental harm, reproductive issues, immune dysfunction, and neurological damage.

• Vulnerable groups such as infants, children, and pregnant women face the greatest risks, especially from contaminants like nitrates, lead, PFAS, microplastics, and TCE.

• Even treated water can contain dangerous byproducts, such as trihalomethanes and chloramines, created during the disinfection process.

Your tap water may not be as safe as you think. Harmful contaminants can slip into your tap water at levels far above what independent researchers consider safe.

And the problem is growing. Dozens of new contaminants are identified every year, and many of them are already turning up in drinking water systems nationwide. 

While the Environmental Protection Agency (EPA) sets legal limits for certain contaminants, those limits don’t always reflect the most current health research. In fact, many EPA Maximum Contaminant Levels are significantly higher than the health-based guidelines recommended by the Environmental Working Group (EWG). 

With that in mind, here’s a closer look at some of the most concerning contaminants showing up in tap water today.

Chloramine is a disinfectant used to treat drinking water that has been in use since the 1930s. More than one in five Americans receive water treated with chloramines.

Many utilities use chloramines because they produce fewer regulated disinfection byproducts than chlorine and provide a longer lasting disinfectant residual. When properly managed, chloramines can help control biofilm, reduce bacterial regrowth, and even lessen taste and odor complaints.

But chloramines come with concerns, especially when levels are not carefully controlled. Chloramines are harder to regulate than chlorine.

Poorly managed treatment can cause:

• Pipe corrosion, which increases the risk of lead and copper leaching

• Nitrification, a chemical process that reduces disinfectant levels and can compromise water quality

• Deterioration of rubber components, such as toilet flapper valves, which may degrade faster than with chlorine

Low levels of chloramine exposure can have irritating effects to the eyes and nose, stomach discomfort, or anemia. 

People undergoing kidney dialysis face some of the highest risks from water treated with chloramines. During dialysis, water comes into direct contact with the bloodstream, which means any chemicals in that water—including chlorine and ammonia—must be removed beforehand. Dialysis centers are required to pretreat and purify the water they use, but if chloramine isn’t fully filtered out, it can destroy red blood cells and lead to hemolytic anemia, a dangerous condition where the blood can’t carry enough oxygen throughout the body.

Hormones and endocrine disruptors make up a large group of natural and synthetic chemicals that influence nearly every function in the body—from growth and metabolism to reproduction and immune health. And while you can’t see, smell, or taste them, these contaminants are increasingly showing up in drinking water. Traces of natural hormones, pharmaceutical residues, and powerful synthetic chemicals are entering water supplies from a surprisingly wide range of sources:

• Human waste: Natural hormones and medications we excrete pass into wastewater and can make their way back into the water supply.

• Improper disposal of medications: Flushing hormonal drugs allows them to enter waterways untreated.

• Agricultural runoff: Livestock given growth hormones excrete them into manure, which washes into rivers and lakes during rainfall.

• Industrial waste: Some industrial processes release hormone-like chemicals if waste isn’t properly treated.

• Landfills: Discarded medications and products can leach into groundwater.

• Personal care products: Cosmetics, lotions, and soaps containing endocrine-disrupting compounds flow down household drains into wastewater.

Even though many of these hormones are naturally occurring in the body, consuming them through drinking water can upset your body's delicate hormonal balance. Low exposure has been linked to: 

• Endocrine disruption: Drinking hormone-contaminated water can lead to various health issues, including reproductive problems, developmental issues, and immune system impairment.

• Reproductive issues: Reduced sperm counts, menstrual irregularities, ovulation problems, and potential effects on conditions like endometriosis.

• Hormone-related cancers: Increased risk of breast cancer, prostate cancer, and other hormone-sensitive cancers.

• Developmental problems: Exposure during pregnancy or early childhood may affect physical and cognitive development.

• Metabolic disorders: Disruption of thyroid and other hormone systems may contribute to obesity and thyroid dysfunction.

Currently, no federal drinking water standards exist for hormones or most endocrine-disrupting chemicals. The EPA has identified several as “contaminants of emerging concern,” but they remain unregulated, meaning utilities are not required to test for them or remove them.

Trihalomethanes (THMs) are a type of disinfection by-product (DBPs) that forms when chlorine or other disinfectants react with natural organic matter in tap water. Common THMs found in drinking water include chloroform, bromoform, bromodichloromethane, and dibromochloromethane. 

While disinfection is essential for safe drinking water, long-term exposure to THMs carries serious health concerns. 

Exposure has been tied to higher rates of bladder and colorectal cancers, and research indicates that drinking water contaminated with THMs during pregnancy may increase the risk of complications, including stillbirth. In addition, some evidence suggests that THMs may affect the central nervous system, influencing how the brain and nerves function.

Currently, the EPA permits up to 80 ppb of THMs in drinking water—hundreds of times higher than the EWG’s recommended 0.15 ppb. This massive gap leaves millions of Americans exposed to levels that may still pose serious health risks.

Arsenic is a naturally occurring mineral found in every state that enters drinking water sources through industrial waste and agricultural runoff. It is recognized as a known carcinogen linked to increased risks of bladder, lung, and skin cancer by the EPA and WHO. Research from the American Heart Association and other health agencies also connects long-term arsenic exposure to cardiovascular disease.

According to the EPA, even low levels of arsenic in drinking water are associated with diabetes, heart and lung problems, and certain cancers. Recent studies have linked high arsenic exposure with increased risk of kidney disease. Children and pregnant women face the greatest risk as studies found that prenatal arsenic exposure can impair cognitive development, contribute to behavioral issues, and weaken the developing immune system.

While the EPA’s current limit is 10 ppb, many scientists argue this standard is far too high. Experts at the EWG and the California Office of Environmental Health Hazard Assessment recommend a far stricter health guideline of 0.004 ppb to better protect against cancer and other long-term harm.

The need for safer limits is urgent: more than 134 million Americans drink water with elevated arsenic levels—and that figure doesn’t include households using private wells.

Nitrates are among the most common drinking water contaminants that often go unnoticed because they are tasteless, odorless, and invisible. Nitrates enter water supplies through agricultural runoff, wastewater, landfills, septic systems, and urban drainage. 

While nitrate contamination is especially common in well water—a U.S. Geological Survey found that almost one-fifth of shallow drinking water wells in agricultural areas likely exceed the legal limit for nitrate—the EWG’s Tap Water Database shows that public systems in both rural and urban areas are affected, with an estimated 263 million people served water that contained nitrates. 

The health risks are especially serious for infants and children. High nitrate levels can cause methemoglobinemia, or “blue baby syndrome,” a potentially life-threatening condition that limits the blood’s ability to carry oxygen. Infants exposed in the womb may face delayed physical and cognitive development. A peer-reviewed EWG study estimated that nitrate exposure may contribute to thousands of cases of very low birth weight, preterm births, and neural tube defects each year. Adults are also at risk—excess nitrate consumption has been linked to nausea, headaches, rapid heartbeat, and gastrointestinal issues.

Despite these dangers, the EPA’s enforceable limit for nitrates remains at 10 ppm. However, growing evidence suggests this standard is not protective enough. The Environmental Working Group recommends a far stricter health guideline of 0.14 ppm to reduce risks related to cancer and fetal development.

Fluoride is added to many public water systems to help prevent cavities, but too much of it can have the opposite effect. Excess fluoride can damage teeth and bones, leading to dental and skeletal fluorosis. In severe cases, fluoride can replace calcium in teeth and bone tissue, causing weakness, brittleness, and deformities. The EWG estimates that up to 40% of Americans show signs of fluorosis, ranging from mild to severe.

Children are especially vulnerable. Long-term ingestion of fluoride above recommended levels increases the risk of dental fluorosis, which causes mottling, pitting, and weakened enamel. Even more concerning, a recent assessment from the National Toxicology Program found that children exposed to higher levels of fluoride in drinking water—above 1.5 ppm—had lower IQ scores, based on studies in populations outside the U.S.

Additional health risks of high fluoride exposure include:

• Thyroid dysfunction: potentially leading to hypothyroidism, which is a condition where the thyroid gland is underactive and doesn’t produce enough hormones. The symptoms of hypothyroidism include weight gain, depression, low energy levels, and additional complications specific to infants, children, and teens. 

• Depletion of calcium in bone structures and higher-than-normal concentrations of calcium in the blood, making bones more susceptible to fractures

• Cardiovascular problems, including arteriosclerosis and arterial calcification, high blood pressure, myocardial damage, cardiac insufficiency, and heart failure

• Reproductive issues, such as lower fertility and early puberty in girls

As of September 2024, a federal ruling determined that fluoride levels at 0.7 ppm still pose a risk of reduced IQ in children, requiring the EPA to take regulatory action under the Toxic Substances Control Act.

In the meantime, the EPA’s maximum legal limit for fluoride remains 4 ppm to prevent severe skeletal fluorosis. But research shows that harm may occur at far lower levels. The Department of Health and Human Services recommends no more than 0.7 ppm, but even that standard is now under scrutiny.

Trichloroethylene (TCE) is a carcinogenic volatile organic compound (VOC) once widely used in industrial and commercial applications. Today, it’s recognized as a human carcinogen through all routes of exposure by the EPA, the International Agency for Research on Cancer, and the Department of Health and Human Services. 

TCE harms the liver, kidneys, immune system, and nervous system, disrupts hormones, and affects male and female reproduction. 

Pregnant women and developing fetuses face the highest risk. TCE can accumulate in breast tissue and cross the placenta, and exposure during pregnancy has been associated with heart defects and other developmental harm. 

Even moderate exposure can cause headaches, dizziness, and neurological symptoms, while higher exposures may lead to severe nerve damage, liver injury, or even death. TCE exposure is also linked to kidney and liver cancer, non-Hodgkin lymphoma, and widespread harm to the reproductive, immune, and nervous systems. It has also been linked to serious neurological disorders like Parkinson’s disease. A JAMA Neurology study found that just two years of heavy TCE exposure increased Parkinson’s risk by 70%. 

Despite these risks, the EPA still permits up to 5 ppb of TCE in drinking water—more than ten times higher than the EWG’s recommended 0.4 ppb, a level aimed at better protecting the immune system.

Microplastics are shreds of plastic that can silently slip into your bloodstream, cling to your organs, and even reach your brain. Due to their size, microplastics can sneak into public water sources and slip through conventional filtration systems at treatment plants, all to end up in your glass of water.

Studies have found that 94% of U.S. tap water samples contained microplastic fibers—and these particles don’t just stay in the environment. Researchers have found microplastics in placental tissue, breast milk, lungs, and even the human brain. Microplastic exposure has also been associated with:

• Heart disease and stroke

• Reproductive issues

• Immune system dysfunction

• Reduced infant birth weight

• Digestive problems, including colon cancer

Despite these findings, the EPA still has no federal limit on microplastic levels in U.S. drinking water. Most concerning of all: researchers say we’re only beginning to understand the full scope of the harm microplastics may cause.

Lead is a toxic metal that still finds its way into millions of American homes through aging lead service lines. As these old pipes corrode, lead can leach directly into drinking water. Even though states are working to replace lead pipes, hundreds of millions of people are still drinking water from water systems reporting problematic lead levels. Major health agencies—including the EPA and the Department of Health and Human Services—recognize lead as a human carcinogen or likely carcinogen.

While lead exposure is dangerous for everyone, children face the greatest risks: lead exposure can cause permanent damage to the developing brains of fetuses and children, resulting in a loss of IQ points, attention deficit hyperactivity disorder, learning problems, low birth weight, and related complications

In adults, it can adversely affect the kidneys and reproductive systems, cause heart disease, and lead to fatal heart attacks, among other harms.

Children are especially vulnerable due to their developing nervous systems. Lead exposure can cause permanent damage to the developing brains of fetuses and children, resulting in a loss of IQ points, attention deficit hyperactivity disorder, learning problems, low birth weight, and related complications. Higher levels can lead to anemia, muscle weakness, and irreversible brain damage. 

Adults aren’t immune either—lead exposure can cause kidney damage, high blood pressure, and reproductive problems.

Despite these risks, the EPA’s action level remains at 15 ppb. Many experts say that’s far from safe. California’s public health goal is just 0.2 ppb—75 times lower—because research shows that even tiny increases in blood lead levels can reduce a child’s IQ.

Perfluoroalkyl and poly-fluoroalkyl substances (PFAS) are a family of toxic chemicals that accumulate in the environment and living organisms, earning them the nickname “forever chemicals.” PFAS accumulates in the environment, in our bodies, and can remain in our bloodstream for decades. In fact, studies show that more than 165 million people are drinking water contaminated with PFAS. 

PFAS pollution is often linked to nearby industrial sites, landfills, airports, and military bases where the chemicals are used or have been used. However, a new California study reveals that even in areas without industrial PFAS manufacturing, people can be significantly exposed to these “forever chemicals” through contaminated drinking water.

PFAS are linked to an alarming list of health problems. The largest epidemiological study ever conducted found associations between PFAS exposure and thyroid disease, high cholesterol, cardiovascular issues, ulcerative colitis, liver damage, hormone disruption, weakened immunity, and cancers of the kidney and testicles. Other research connects PFAS exposure to DNA damage and more severe COVID-19 symptoms.

Pregnant women, infants, and children face even greater risks. PFAS exposure has been linked to skeletal abnormalities, low birth weight, miscarriage, high blood pressure during pregnancy, reduced vaccine response, early puberty, decreased fertility later in life, and developmental problems.

In April 2024, the EPA set the first-ever enforceable drinking water limits for six PFAS. The new standards included:

• 4 ppt for PFOA and PFOS

• 10 ppt for PFHxS, PFNA, and GenX

• A Hazard Index of 1 for mixtures including PFBS

But on May 14, 2025, the EPA announced two major changes:

1. Delayed enforcement: Water utilities now have until 2031—two years longer than planned—to meet the 4 ppt limits for PFOA and PFOS.

2. Rescinded limits: The EPA is reconsidering the proposed limits for PFHxS, PFNA, GenX, and the Hazard Index for these chemicals.

The contaminants outlined above aren’t hypothetical—they’re already in tap water nationwide, often at levels far above what health experts consider safe. A powerful, trusted filter is one of the simplest ways to protect the people you love.

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