Complete Guide to Drinking Water Contaminants

Your drinking water travels a long journey before reaching your tap. Along the way, it can pick up hundreds of different contaminants from natural sources, industrial pollution, agricultural runoff, and aging infrastructure. The Environmental Protection Agency (EPA) regulates over 90 contaminants under the Safe Drinking Water Act, but thousands more remain unregulated.

According to the EPA, approximately 7% of the U.S. population is served by community water systems that violated health-based standards in 2023. Even in systems that meet federal standards, contaminants can still be present at levels that concern health experts, particularly for vulnerable populations like children, pregnant women, and those with compromised immune systems.

This comprehensive guide examines the most common and concerning drinking water contaminants, their sources, health effects, current regulations, and most importantly, how to remove them from your water.

What It Is and Where It Comes From

Lead is a toxic heavy metal that was widely used in plumbing materials until 1986. Despite being banned in new construction, lead contamination remains a critical issue due to:

• Lead service lines connecting homes to water mains (estimated 6-10 million still in use across the U.S.)
• Lead solder in older plumbing systems
• Brass fixtures that can contain up to 8% lead
• Corrosive water that leaches lead from pipes (as seen in Flint, Michigan)

Health Effects

Lead exposure is particularly dangerous because there is no safe level, especially for children. Health impacts include:

• In children: Developmental delays, learning difficulties, reduced IQ, behavioral problems, slowed growth, hearing problems, and anemia
• In adults: Cardiovascular effects, increased blood pressure, kidney damage, reproductive problems, and potential impacts on the nervous system
• In pregnant women: Risk of reduced fetal growth and premature birth

The Centers for Disease Control and Prevention (CDC) estimates that at least 4 million households have children being exposed to high levels of lead.

Current Regulations

The EPA's Lead and Copper Rule sets an action level of 15 parts per billion (ppb). However, the American Academy of Pediatrics and other health organizations advocate for much stricter standards, noting that no level of lead is safe for children.

Removal Methods

• Reverse osmosis: Removes 94-97% of lead (most effective)
• Activated carbon filters: Remove 95%+ when certified for lead
• Distillation: Removes 99%+ of lead
• NSF/ANSI 53 certified filters: Proven to reduce lead to safe levels

Pro tip: Flushing your tap for 30-60 seconds before use can significantly reduce lead levels if the contamination source is your home's plumbing.

What They Are

Per- and polyfluoroalkyl substances (PFAS) are a group of over 12,000 synthetic chemicals used since the 1940s in industrial applications and consumer products. They're called "forever chemicals" because they don't break down in the environment or the human body.

Common sources include firefighting foam, non-stick cookware, water-resistant fabrics, food packaging, and industrial manufacturing. The CDC reports that PFAS are detected in the blood of 97% of Americans.

Health Effects

Extensive research by the EPA and health organizations has linked PFAS exposure to:

• Increased cholesterol levels
• Changes in liver enzymes
• Decreased vaccine response in children
• Increased risk of kidney and testicular cancer
• Thyroid disease and hormone disruption
• Pregnancy-induced hypertension and preeclampsia
• Lower infant birth weights

Current Regulations

In 2024, the EPA established the first-ever national drinking water standards for six PFAS compounds, setting maximum contaminant levels (MCLs) at 4 parts per trillion (ppt) for PFOA and PFOS. This represents one of the strictest drinking water standards ever set.

Removal Methods

• Reverse osmosis: Removes 90-95% of PFAS (most effective home method)
• Activated carbon filters: Remove 70-90% depending on contact time and carbon type
• Ion exchange systems: Effective for specific PFAS compounds
• NSF P473 certified filters: Specifically tested for PFAS reduction

Learn more in our dedicated PFAS Forever Chemicals Guide.

Sources of Contamination

Arsenic is a naturally occurring element found in rocks and soil that can dissolve into groundwater. It's particularly prevalent in:

• Western states including Arizona, New Mexico, Nevada, and parts of California
• Agricultural areas where arsenic-based pesticides were historically used
• Areas with mining operations
• Regions with certain geological formations

The U.S. Geological Survey estimates that approximately 2.1 million people in the United States rely on domestic wells with arsenic concentrations exceeding the EPA standard.

Health Effects

Long-term arsenic exposure is associated with serious health conditions:

• Cancer: Increased risk of bladder, lung, and skin cancer
• Cardiovascular disease: Higher rates of heart disease and stroke
• Diabetes: Increased risk of type 2 diabetes
• Skin conditions: Discoloration, lesions, and hardened patches
• Neurological effects: Potential developmental issues in children

Regulations

The EPA's maximum contaminant level (MCL) for arsenic is 10 ppb. However, the World Health Organization and many health advocates argue that even this level poses cancer risks, estimating that 1 in 500 people exposed to 10 ppb of arsenic over a lifetime will develop cancer.

Removal Methods

• Reverse osmosis: Removes 95-98% of arsenic
• Distillation: Removes 98%+ of arsenic
• Activated alumina filters: Effective for arsenic removal
• Ion exchange: Effective but requires pH adjustment

Sources

Nitrates enter drinking water primarily through:

• Agricultural runoff: Fertilizers and animal waste from farms
• Septic systems: Improperly maintained or failing systems
• Wastewater treatment discharge
• Erosion of natural deposits

Agricultural regions, particularly in the Midwest, California's Central Valley, and other intensive farming areas, commonly experience elevated nitrate levels in groundwater.

Health Effects

Nitrate contamination poses specific risks:

• Blue baby syndrome (methemoglobinemia): A potentially fatal condition in infants under 6 months where nitrates interfere with the blood's ability to carry oxygen
• Potential cancer risk: Some studies suggest links to colorectal cancer and thyroid disease
• Birth defects: Possible association with neural tube defects and other developmental issues

Regulations

The EPA's MCL for nitrates is 10 milligrams per liter (mg/L), measured as nitrogen. Pregnant women and families with infants should be particularly vigilant about nitrate levels.

Removal Methods

• Reverse osmosis: Removes 85-95% of nitrates
• Distillation: Effective nitrate removal
• Ion exchange: Specifically effective for nitrates
• Note: Standard carbon filters do NOT remove nitrates

Important: Boiling water concentrates nitrates and makes the problem worse. Never boil water with high nitrate levels for infant formula.

What It Is

Hexavalent chromium (chromium-6) is a toxic form of the element chromium made famous by the Erin Brockovich case. It enters water supplies through:

• Industrial manufacturing and metal processing
• Leather tanning operations
• Cooling towers
• Paint and dye manufacturing
• Natural erosion in certain geological areas

A 2016 Environmental Working Group study found chromium-6 in drinking water supplies serving over 218 million Americans in all 50 states.

Health Effects

• Cancer: Classified as a known human carcinogen; linked to lung cancer when inhaled and potentially stomach cancer when ingested
• Liver and kidney damage
• Reproductive and developmental harm
• Skin irritation and allergic reactions

Regulations

Currently, the EPA regulates total chromium at 100 ppb but does not have a specific standard for the more toxic chromium-6. California set a state standard of 10 ppb for chromium-6 specifically. Many health advocates argue for a federal standard below 1 ppb based on cancer risk assessments.

Removal Methods

• Reverse osmosis: Removes 95-98% of chromium-6
• Ion exchange: Highly effective
• Distillation: Removes chromium-6 effectively

Common Microbial Contaminants

Biological contaminants pose immediate health risks and include:

• E. coli and coliform bacteria: Indicators of fecal contamination
• Cryptosporidium and Giardia: Parasites resistant to chlorine disinfection
• Legionella: Bacteria that can cause severe pneumonia
• Viruses: Including norovirus, hepatitis A, and rotavirus

Sources

• Sewage overflows and wastewater treatment failures
• Agricultural runoff containing animal waste
• Failing septic systems
• Wildlife contamination of surface water
• Biofilm growth in aging distribution systems

Health Effects

Symptoms range from mild to severe and include:

• Gastrointestinal illness (diarrhea, vomiting, cramps)
• Respiratory infections
• Potentially life-threatening conditions in immunocompromised individuals
• Chronic issues from parasite infections

Removal Methods

• UV purification: Kills 99.99% of bacteria, viruses, and parasites
• Reverse osmosis: Physically removes microorganisms
• Distillation: Kills pathogens through boiling
• Boiling: One minute of rolling boil (3 minutes above 6,500 feet elevation)
• NSF/ANSI 53 or 58 certified filters

Common Pesticides in Water

• Atrazine: One of the most widely used herbicides in the U.S., particularly in corn production
• Glyphosate (Roundup): The most commonly used agricultural chemical globally
• 2,4-D: Broadleaf herbicide
• Chlorpyrifos: Insecticide used on various crops

Health Concerns

• Endocrine disruption: Particularly atrazine, which can interfere with hormones
• Cancer risk: Some pesticides classified as probable carcinogens
• Reproductive effects: Birth defects and developmental issues
• Neurological impacts: Particularly in children

Regulations

The EPA sets MCLs for specific pesticides. For example, atrazine is limited to 3 ppb, though the European Union banned it due to groundwater contamination concerns.

Removal Methods

• Activated carbon filters: Highly effective for most pesticides (80-95% reduction)
• Reverse osmosis: Removes most pesticides
• Granular activated carbon (GAC): Particularly effective with longer contact time

The Emerging Threat

Pharmaceutical contamination is an emerging concern that's largely unregulated. Common medications found in drinking water include:

• Antibiotics
• Hormones (including birth control)
• Antidepressants
• Pain relievers
• Cholesterol medications

A U.S. Geological Survey study detected pharmaceuticals in 80% of streams tested across the country.

Sources

• Excretion by humans and animals taking medications
• Improper disposal of unused medications
• Wastewater treatment plants not designed to remove pharmaceuticals
• Agricultural runoff from livestock operations

Potential Health Effects

While concentrations are typically very low (measured in parts per trillion), concerns include:

• Long-term cumulative effects
• Hormone disruption from contraceptive residues
• Antibiotic resistance development
• Unknown synergistic effects of multiple pharmaceuticals

Removal Methods

• Reverse osmosis: Most effective (90-99% removal for most pharmaceuticals)
• Activated carbon: Effective for many but not all pharmaceuticals
• Advanced oxidation: Available in some whole-house systems

Note: Standard municipal treatment is not designed to remove pharmaceuticals, making point-of-use filtration important for concerned households.

The Treatment Paradox

When chlorine and other disinfectants used to kill bacteria react with natural organic matter in water, they form potentially harmful byproducts:

• Trihalomethanes (THMs): Including chloroform
• Haloacetic acids (HAAs)
• Chlorite and bromate: From chlorine dioxide and ozone treatment

Health Concerns

• Increased cancer risk (bladder, colorectal)
• Reproductive effects including miscarriage and birth defects
• Liver and kidney damage at high levels

Regulations

The EPA sets MCLs for total trihalomethanes at 80 ppb and haloacetic acids at 60 ppb. However, levels often fluctuate seasonally, with higher concentrations in summer months.

Removal Methods

• Activated carbon filters: Very effective for THMs and HAAs
• Reverse osmosis: Removes most DBPs
• Letting water sit: Some volatile THMs will dissipate if water sits uncovered

Step 1: Know Your Water

• Request your utility's Consumer Confidence Report (CCR)
• Check your local water quality data
• Consider professional testing for contaminants not in the CCR
• Test annually if you have a private well

Read our guide on Understanding Your Water Quality Report for detailed information.

Step 2: Identify Your Specific Risks

• Older homes (pre-1986): Lead risk from pipes and solder
• Agricultural areas: Nitrates, pesticides, atrazine
• Industrial areas: Chromium-6, industrial solvents, PFAS
• Western/arid regions: Arsenic from natural sources
• Military base proximity: PFAS from firefighting foam

Step 3: Choose Appropriate Treatment

Not all filters remove all contaminants. Match your filtration to your specific needs:

• For lead: NSF/ANSI 53 certified carbon filter or reverse osmosis
• For PFAS: Reverse osmosis or NSF P473 certified filters
• For arsenic: Reverse osmosis or distillation
• For bacteria: UV purification or reverse osmosis
• For multiple contaminants: Reverse osmosis system (most comprehensive)

See our Complete Water Filter Buying Guide for detailed comparisons.

Step 4: Maintain Your Treatment System

• Replace filters according to manufacturer recommendations
• Annual testing to verify treatment effectiveness
• Professional maintenance for complex systems
• Keep records of filter changes and test results

What are the most dangerous water contaminants?

Lead, arsenic, and certain bacteria/parasites pose the most immediate health risks. Lead has no safe level for children, arsenic is a known carcinogen, and microbial contamination can cause acute illness. PFAS are increasingly concerning due to their persistence and widespread presence.

Can I trust my municipal water supply?

Most municipal water in the U.S. is safe and meets EPA standards. However, "meets standards" doesn't mean contaminant-free. Aging infrastructure, unregulated emerging contaminants, and variations in individual sensitivity mean additional home filtration may be warranted, especially for vulnerable populations.

How often should I test my water?

If you have municipal water, review your annual CCR. Additional testing is recommended if you: have a private well (test annually), are pregnant or have young children, live in an older home (test for lead), notice changes in water taste/smell, or live near agricultural/industrial areas.

Are expensive filters worth it?

It depends on your water quality and health concerns. A $30 pitcher filter may be sufficient if you only need to improve taste and reduce chlorine. However, if testing reveals lead, arsenic, or PFAS, investing in a certified reverse osmosis system ($200-500) provides comprehensive protection that's worth the cost.

What if my water meets EPA standards but I'm still concerned?

EPA standards are designed for the general population and may not account for sensitive individuals, cumulative effects, or emerging research. If you have health concerns, are pregnant, have young children, or are immunocompromised, additional filtration provides an extra margin of safety.

Do I need different filters for different contaminants?

Some filters are specialized, but reverse osmosis systems remove 95-99% of most contaminants, making them a comprehensive solution. For specific concerns (like just lead or just chlorine taste), targeted filters may be more cost-effective.

Understanding drinking water contaminants is the first step in protecting your family's health. While the presence of contaminants in drinking water can be concerning, effective solutions exist for nearly every water quality issue.

The key is to:

1. Know what's in your water through testing and reviewing reports
2. Understand which contaminants pose the greatest risk to your household
3. Select appropriate, certified treatment systems
4. Maintain those systems properly
5. Stay informed about emerging contaminants and changing regulations

Remember, you don't have to accept whatever water comes out of your tap. With the right information and tools, you can ensure your drinking water is as safe as possible.