What's in Your Water? The Most Common Contaminants and Their Health Effects

U.S. tap water contains an average of 6 to 30 contaminants that exceed science-based health guidelines, even when it meets EPA legal standards. The most common are lead (a neurotoxin with no safe exposure level), PFAS "forever chemicals" (linked to cancer and hormonal disruption), arsenic, hexavalent chromium, disinfection byproducts (linked to bladder cancer), and nitrates. The gap between what is legally allowed and what science considers safe can be as large as 2,500 times, which is why home filtration is the last line of defense for your family.

Your tap water might look clean. It might smell fine. It might taste perfectly normal. And yet, it can contain dozens of contaminants you can't see, smell, or taste -- but that your body absorbs with every glass you drink.

According to the Environmental Working Group (EWG), public water systems across the United States contain an average of 6 to 30 contaminants that exceed science-based health guidelines. We're not talking about water that violates the law. We're talking about water that meets EPA legal standards but that modern science considers unsafe for long-term consumption.

We've analyzed water quality reports from more than a dozen metropolitan areas we serve, from Dallas-Fort Worth to Michigan, from New Jersey to Denver. The patterns are clear: the same contaminants show up again and again. And the health risks are well documented.

This article covers the six most common contaminants in U.S. drinking water, backed by real data from specific cities and states. This isn't meant to scare you. It's meant to give you the information you need to make informed decisions about the water your family drinks.

Lead: the contaminant that should never be in your water

• No safe level of exposure -- EPA's own goal for lead is zero
• Enters from old pipes installed before 1986, not from the water source
• Causes permanent brain damage in children under 6, who absorb it 4-5x more efficiently than adults
• Found in virtually every territory from Philadelphia (20,000+ lead service lines) to Michigan (Flint crisis)

Lead is one of the most dangerous contaminants that can be in drinking water, and there is no safe level of exposure. None. The EPA itself acknowledges that its Maximum Contaminant Level Goal (MCLG) for lead is zero.

Where it comes from

Lead isn't in the water at the source. It enters when water passes through lead pipes, lead solder, or lead service lines that connect the main water line in the street to your house. Many of these pipes were installed 50, 80, or even 100 years ago, and they're still in use today.

Where we find it

Lead contamination isn't an isolated problem. We've documented it across virtually every territory we serve:

• Philadelphia: More than 20,000 active lead service lines still deliver water to homes. The city has one of the largest inventories of lead pipes in the Northeast.
• New Jersey: Newark's lead crisis in 2019 revealed levels 8 times above the EPA's action level of 15 ppb. Thousands of emergency filters were distributed and the city fast-tracked a pipe replacement program costing over $120 million.
• Michigan: The Flint water crisis that began in 2014 exposed more than 100,000 residents to elevated lead levels. Years later, the pipe replacement process continues, and public trust in tap water remains damaged.
• Dallas-Fort Worth: Lead has been detected in older distribution systems, particularly in neighborhoods with infrastructure predating 1986.
• Indiana, Connecticut, Virginia, and Maryland: All report lead detections in their annual water quality reports.
• Michiana: The lead crisis in Benton Harbor -- just 45 miles away -- affected thousands of homes and serves as a reminder of how close the problem can be.

Health effects

Lead is a neurotoxin. There is no scientific debate about this. Lead exposure causes:

• In children: Irreversible brain development damage, learning disabilities, reduced IQ, behavioral problems. Children under 6 are most vulnerable because their bodies absorb lead 4 to 5 times more efficiently than adults.
• In adults: High blood pressure, kidney damage, reproductive problems, joint and muscle pain.
• In pregnant women: Lead can cross the placental barrier, affecting fetal development and increasing the risk of premature birth.

The most important point: neurological damage from lead exposure in children is permanent. It doesn't reverse. That's why prevention is the only effective strategy.

PFAS: the "forever chemicals" that are everywhere

• 14,000+ synthetic chemicals that never break down in the environment or human body
• Classified as a confirmed carcinogen (Group 1) by IARC in 2024
• Present in every territory served, with Michigan having 200+ contaminated sites
• EPA limit is 4 parts per trillion -- but science suggests no truly safe level exists

If there's one contaminant that defines the U.S. water crisis of this decade, it's PFAS. These per- and polyfluoroalkyl substances are a group of more than 14,000 synthetic chemicals that don't break down -- not in the environment, not in your body. That's why they're called "forever chemicals."

For a deeper dive into PFAS specifically, check out our complete guide to PFAS in drinking water.

Where they come from

PFAS were used for decades in the manufacturing of nonstick products, water repellents, firefighting foams, and food packaging. The primary sources of water contamination include:

• Military bases: Aqueous film-forming foams (AFFF) used for decades in training exercises and emergencies at military installations are one of the largest sources of PFAS contamination nationwide.
• Factories and industrial facilities: Plants that manufactured or used PFAS discharged waste that leached into groundwater.
• Airports and fire stations: Where AFFF firefighting foams were used.
• Landfills: Products containing PFAS are disposed of in landfills, and leachate contaminates nearby water sources.

Where we find it

PFAS are present in every single territory we serve. No exceptions:

• Michigan: With more than 200 confirmed PFAS contamination sites, Michigan has the highest number of contaminated sites in the entire country. This includes military bases, industrial zones, and rural communities whose groundwater has been affected.
• New Jersey: Military bases McGuire and Fort Dix have been identified as major sources of PFAS contamination. New Jersey was one of the first states to establish state-level limits stricter than federal standards.
• Maryland: A total of 65 community water systems have reported PFAS detections, affecting hundreds of thousands of people.
• Denver: Buckley Space Force Base in Aurora has been identified as a source of PFAS contamination in the metropolitan area's groundwater.
• Virginia: Multiple military installations, including Langley, Fort Belvoir, and Quantico, have contaminated local water sources with PFAS.
• Connecticut: The Groton Naval Base is linked to PFAS contamination in the region.
• Indiana: Crane Naval Base has been identified as a source of PFAS in the southern part of the state's groundwater.
• Delaware, Dallas, Philadelphia: All report PFAS detections in their water systems.

Health effects

In 2024, the International Agency for Research on Cancer (IARC) classified PFOA, one of the most common PFAS chemicals, as a confirmed human carcinogen (Group 1). Documented health effects include:

• Cancer: Kidney, testicular, thyroid, and breast cancer.
• Hormonal disruption: Endocrine system disruption, thyroid problems, reduced fertility.
• Immune system: Reduced vaccine response, particularly in children.
• Liver: Liver damage and elevated cholesterol levels.
• Child development: Low birth weight and developmental delays.

The EPA's legal limit for individual PFAS compounds is 4 parts per trillion (ppt). But the science suggests there is no truly safe level of cumulative exposure to chemicals that never break down.

Arsenic: a natural poison in your water

• Occurs naturally in rock formations and dissolves into groundwater
• WHO Group 1 carcinogen -- linked to skin, lung, bladder, kidney, and liver cancer
• EWG guideline is 2,500x stricter than the EPA legal limit (0.004 ppb vs 10 ppb)
• Found in Los Angeles, Eagle Mountain (Utah), and Rio Grande Valley (Texas)

When most people think of arsenic, they think of mystery novels. But arsenic is a real and present contaminant in the drinking water of millions of Americans -- and most of it enters the water completely naturally.

Where it comes from

Arsenic occurs naturally in the Earth's crust. When groundwater flows through rock formations containing arsenic, it dissolves and carries it into the wells and aquifers that feed public water systems. It can also enter water through mining activities, historical arsenic-based pesticide use, and metal smelting operations.

Where we find it

• Los Angeles, California: Detected arsenic levels exceed EWG health guidelines, though they remain within the EPA's legal limit of 10 ppb. The gap between "legal" and "safe" is exactly the problem we'll address later in this article.
• Eagle Mountain, Utah: The natural geology of the Utah Valley produces arsenic in the region's groundwater sources.
• Rio Grande Valley, Texas: Levels of up to 3 ppb of arsenic have been detected, originating from the natural geology of the Rio Grande basin.

Health effects

Chronic exposure to arsenic in drinking water -- even at levels the EPA considers "safe" -- has been linked to:

• Cancer: Skin, lung, bladder, kidney, and liver cancer. The World Health Organization classifies arsenic as a Group 1 carcinogen.
• Cardiovascular disease: Increased risk of heart disease and hypertension.
• Diabetes: Studies have found a correlation between chronic arsenic exposure and the development of type 2 diabetes.
• Skin problems: Skin lesions, pigmentation changes, and skin thickening (keratosis).
• Child development: Affects cognitive development and can cause learning problems.

The EWG health guideline for arsenic is 0.004 ppb -- that's 2,500 times stricter than the EPA's legal limit of 10 ppb. That gap should concern you.

Chromium-6 (hexavalent chromium): the "Erin Brockovich" chemical

• Present in the water of 200+ million Americans across all 50 states
• No specific EPA legal limit exists -- only total chromium is regulated
• EWG recommends 0.02 ppb vs EPA's 100 ppb total chromium limit (5,000x gap)
• Linked to stomach and intestinal cancer when ingested

If you've seen the movie "Erin Brockovich" starring Julia Roberts, you already know this contaminant. But what you might not know is that hexavalent chromium isn't a problem limited to a small town in California. It's in the drinking water of most Americans.

Where it comes from

Chromium-6 enters water through two pathways:

• Natural: Erosion of natural chromium deposits in the Earth's crust.
• Industrial: Steel plants, leather tanneries, textile factories, wood treatment plants, and chrome plating operations. Industrial waste is the more problematic source because it produces higher concentrations.

Where we find it

• Los Angeles, California: Has been one of the cities with the highest detected levels of chromium-6, consistent with Southern California's industrial history.
• Denver, Colorado: Denver's water contains detectable levels of hexavalent chromium.
• Philadelphia: The city's industrial history contributes to the presence of chromium-6 in its water system.
• Virginia: Multiple water systems have reported chromium-6 detections.

An EWG study found that chromium-6 is present in the drinking water of more than 200 million Americans across all 50 states. This isn't a regional problem. It's a national one.

Health effects

• Cancer: When ingested, chromium-6 can cause stomach and intestinal cancer. The EPA classifies it as a known carcinogen when inhaled, and the evidence for the oral pathway is strong.
• Liver and kidney: Damage to these organs with chronic exposure.
• Reproductive system: Animal studies show adverse reproductive effects.
• Development: Potential effects on fetal development.

The chromium-6 problem is particularly frustrating because the EPA has no specific legal limit for hexavalent chromium. It only regulates total chromium (chromium-3 + chromium-6 combined) at a limit of 100 ppb. The EWG recommends a maximum of 0.02 ppb for chromium-6 alone. That's a difference of 5,000 times.

Disinfection byproducts (TTHMs and HAA5s): the hidden cost of "clean" water

• Created during chlorination when disinfectants react with organic matter in water
• 20-40% increased bladder cancer risk with chronic exposure to trihalomethanes
• Present in virtually every chlorinated water system in the United States
• Solution is post-treatment filtration -- removing byproducts after disinfection, before your glass

Here's the paradox: to make water "safe," treatment plants add chlorine and chloramines to kill bacteria and pathogens. That's necessary and it saves lives. But when those disinfectants react with natural organic matter in the water -- leaves, algae, soil -- they create chemical compounds called disinfection byproducts, or DBPs.

The two main groups are:

• TTHMs (total trihalomethanes): Including chloroform, bromodichloromethane, dibromochloromethane, and bromoform.
• HAA5s (haloacetic acids): A group of five acids that form during chlorination.

Where we find them

Disinfection byproducts are present in virtually every water system that uses chlorine, which is the vast majority. But some territories show particularly elevated levels:

• Dallas-Fort Worth: With 17 contaminants above health guidelines, disinfection byproducts are among the most concerning in the DFW area. Dallas water has 38 detected contaminants in total.
• New Jersey: TTHMs and HAA5s are consistently detected across multiple water systems statewide.
• Philadelphia: Water from the Schuylkill and Delaware rivers, with their organic matter load, produces significant levels of DBPs when disinfected.
• Denver: Quality reports show detectable levels of TTHMs and HAA5s.
• Indiana, Michigan, Connecticut, Virginia: All report disinfection byproducts in their water quality analyses.
• Rio Grande Valley, Texas: The high organic load in Rio Grande water contributes to the formation of these byproducts.

Health effects

• Bladder cancer: The strongest and most consistent association in the scientific literature. Epidemiological studies have found a 20-40% increased risk of bladder cancer with chronic TTHM exposure.
• Colorectal cancer: Growing evidence of an association.
• Reproductive problems: Miscarriage, low birth weight, and neural tube defects have been linked to DBP exposure during pregnancy.
• Liver and kidney: Damage with long-term exposure.

This creates a real dilemma: you need disinfection to prevent acute bacterial illness, but the disinfection process creates contaminants that increase chronic disease risk. The solution isn't to stop disinfecting. The solution is to filter out the byproducts after disinfection, before the water reaches your glass.

Nitrates: agriculture's silent threat

• Colorless, odorless, and tasteless -- impossible to detect without laboratory analysis
• Can cause "blue baby syndrome" (methemoglobinemia) in infants under 6 months
• Linked to multiple cancers at levels below the EPA legal limit of 10 mg/L
• Primary sources: agricultural fertilizers, livestock runoff, and leaking septic systems

Nitrates are nitrogen compounds that enter water primarily through agricultural activity. They're colorless, odorless, and tasteless, making them impossible to detect without laboratory analysis.

Where they come from

• Agricultural fertilizers: The primary source. Nitrogen applied to fields leaches into groundwater.
• Livestock runoff: Animal waste from farming operations contributes nitrates to surface water and groundwater.
• Septic systems: Leaking septic tanks can contaminate nearby wells.
• Herbicides: In agricultural areas like Indiana, atrazine (an herbicide) is detected alongside nitrates.

Where we find them

• Indiana: Nitrates from agricultural runoff are a primary contaminant, along with atrazine. The intensive farming of the Midwest is the source.
• Michiana: Surrounding agricultural counties contribute nitrates that exceed health guidelines in wells throughout the region.
• New Jersey: The state's population and agricultural density generates significant nitrate levels in many water systems.
• Maryland: Proximity to the Chesapeake Bay watershed and agricultural activity contribute to nitrate levels.
• Michigan: The state's agriculture contributes to nitrate levels, especially in rural communities dependent on wells.

Health effects

• Blue baby syndrome (methemoglobinemia): The most well-known risk. In infants under 6 months, nitrates can interfere with the blood's ability to carry oxygen, causing a potentially fatal condition. If you have a baby at home, water quality becomes even more critical. Read more in our article about your baby and tap water.
• Cancer: Recent studies have linked chronic nitrate exposure to colorectal, ovarian, thyroid, kidney, and bladder cancer -- even at levels below the EPA's legal limit.
• Thyroid problems: Nitrates can interfere with iodine uptake by the thyroid.
• Birth defects: Studies suggest increased risk of neural tube defects with nitrate exposure during pregnancy.

The EPA's legal limit for nitrates is 10 mg/L (as nitrogen). But research from the National Cancer Institute and other agencies has found elevated cancer risks at levels well below that legal limit.

Hard water: not a contaminant, but it matters

While not a health contaminant in the strict sense, water hardness deserves mention because it directly affects quality of life, the lifespan of your appliances, and your wallet. Hard water contains high levels of calcium and magnesium that cause scale buildup.

The numbers tell the story:

• Eagle Mountain, Utah: 310 PPM hardness. That's extremely hard -- more than double the national average.
• Rio Grande Valley, Texas: 270 PPM hardness, classified as very hard.
• Michiana, Michigan: 230 PPM, nearly double the national average.
• New Jersey: 190 PPM, significantly above the "hard" threshold of 120 PPM.

Hard water destroys water heaters (reducing their lifespan by 30-50%), leaves residue on dishes and faucets, dries out skin and hair, and reduces the effectiveness of soaps and detergents. If you've noticed your skin isn't improving with lotions, it might be your water.

To better understand the difference between a softener and a filter, check out our guide to water softeners vs. filters.

Why "legal" doesn't mean "safe"

This is perhaps the most important point in this entire article.

The EPA's legal limits (called MCLs, or Maximum Contaminant Levels) were established decades ago and are updated very infrequently. Many of these limits were set in the 1990s or even earlier, based on the science available at the time and what was technically feasible for treatment plants.

The EWG (Environmental Working Group) establishes health guidelines based on the most current science, without factoring in economic or technical feasibility considerations. The difference between the two is dramatic:

| Contaminant | EPA Legal Limit | EWG Health Guideline | Difference |

|---|---|---|---|

| Arsenic | 10 ppb | 0.004 ppb | 2,500x |

| Chromium-6 | No specific limit | 0.02 ppb | N/A |

| Lead | 15 ppb (action level) | 0 ppb | Infinite |

| PFOS/PFOA | 4 ppt each | Lowest detectable | - |

| TTHMs | 80 ppb | 0.8 ppb | 100x |

| HAA5s | 60 ppb | 0.1 ppb | 600x |

| Nitrates | 10 mg/L | ~0.14 mg/L | 70x |

When your water utility tells you the water "meets all federal standards," that's technically true. But it doesn't mean the water is safe according to current science.

The water in Dallas-Fort Worth has 17 contaminants above EWG health guidelines. The water is legal. But 17 contaminants exceed what science considers safe. That distinction matters.

What you can do to protect your family

The good news is you're not powerless. There are concrete steps you can take:

1. Know your water

The first step is knowing exactly what's in your water. The annual Consumer Confidence Reports published by your water utility are a starting point, but they don't tell the whole story. They don't test for every contaminant, and the data may be a year or more old.

A water analysis at your home gives you current, specific data about what's actually coming out of your faucet -- including what gets added between the treatment plant and your glass.

2. Understand that point-of-use filtration is the last line of defense

Even if your city does a good job treating water, contaminants can enter between the treatment plant and your faucet: lead pipes, corroded plumbing, contaminants that municipal treatment doesn't remove (like PFAS and chromium-6).

A home filtration system is the last barrier between contaminants and your family.

3. Don't rely solely on pitcher filters

Brita-style pitcher filters improve taste, but they have limited ability to remove contaminants like PFAS, lead, or chromium-6. A certified point-of-entry or point-of-use filtration system is far more effective.

4. Get a free water test

You can't manage what you don't measure. A professional water analysis tells you exactly which contaminants are present and at what concentrations. With that information, you can make informed decisions about what kind of treatment system you need.

For more information about common water quality questions, visit our frequently asked questions page.

Frequently Asked Questions

What are the most dangerous contaminants in U.S. drinking water?

The six most common and dangerous contaminants are lead (a neurotoxin with no safe level), PFAS forever chemicals (linked to cancer and immune system damage), arsenic (a Group 1 carcinogen), hexavalent chromium (found in the water of over 200 million Americans), disinfection byproducts like trihalomethanes (linked to bladder cancer), and nitrates (dangerous for infants and linked to multiple cancers).

Why does "legal" water not mean "safe" water?

EPA legal limits (MCLs) were established decades ago based on older science and what was technically feasible for treatment plants. The Environmental Working Group's health guidelines, based on current research, are dramatically stricter -- for example, the EWG guideline for arsenic is 2,500 times lower than the EPA legal limit, and for trihalomethanes it is 100 times lower.

Does boiling tap water remove contaminants?

Boiling water kills bacteria and viruses but does not remove chemical contaminants like lead, PFAS, arsenic, chromium-6, or nitrates. In fact, boiling can concentrate some contaminants by evaporating part of the water volume. Only a certified filtration system using technologies like reverse osmosis, activated carbon, or ion exchange can remove these chemicals.

How do I find out what contaminants are in my water?

Start by reviewing your municipality's annual Consumer Confidence Report and checking the EWG database (ewg.org/tapwater) with your zip code. For the most accurate results, request a professional in-home water test, since water quality can change between the treatment plant and your faucet due to pipe conditions, home age, and location within the distribution system.

Can a home water filter remove lead and PFAS?

Yes. A certified whole-house filtration system or reverse osmosis unit can reduce lead by more than 99% and remove up to 90-99% of PFAS. Look for systems with NSF/ANSI 53 certification for lead and NSF/ANSI 58 for reverse osmosis. Basic pitcher filters have limited ability to remove these contaminants and should not be relied upon as your primary defense.

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