Is Your Drinking Water Safe? Hidden Contaminants in U.S. Tap Water

Photography by Treddy Chen @tchen_7993

15 Toxins Found in Drinking Water and Health Effects

Every drop of water we drink carries a story. While water is essential to life, keeping us hydrated, aiding digestion, supporting nutrient absorption, and helping us fight illness, it is rarely pure. All water contains some level of impurities. The real danger comes when toxic chemicals build up in quantities that put our health at risk.

Millions of Americans are exposed to unsafe drinking water each year. Unlike visible pollutants, many of these contaminants cannot be seen, smelled, or tasted. Industrial dumping, pesticide runoff, and outdated federal safety laws have left gaps in our protection, turning a life-giving resource into a potential hazard with lifelong health consequences.

How Contaminants Enter Our Water

Contamination can seep in silently. When underground pipes burst or are repaired, soil and debris can enter the water system. Corroding pipes can also release toxic lead into tap water, a threat that has made national headlines in recent years. Even routine water use may expose families to unseen risks.

A common misconception is that boiling water makes it completely safe. While boiling is effective at killing parasites, bacteria, and viruses, it does nothing to remove chemical pollutants. In fact, it can actually make things worse: as water evaporates, the concentration of certain toxins increases. Combined with aging, poorly maintained infrastructure, this leaves communities vulnerable to water quality that falls below safe standards.

The Chemicals We Don’t Regulate

Not all contaminants are monitored under current regulations. For example, dangerous “forever chemicals," perfluorinated compounds known as PFAS, have been found in tap water across the globe. These chemicals are linked to cancer, thyroid disease, and developmental problems, yet because they are not regulated in many systems, their presence doesn’t trigger violations of official water quality standards.

Other harmful substances that can end up in drinking water include disinfection byproducts, industrial solvents, pesticides, naturally occurring minerals like arsenic, and radioactive elements such as radium. Over time, these contaminants can accumulate in the body and contribute to chronic diseases, including cancer.

The Most Vulnerable Among Us

Children face the greatest risks. Because they consume more water relative to their body weight, and because their bodies are still developing, they are especially susceptible to the harmful effects of contaminated drinking water. For them, exposure to toxins can mean a higher chance of disease later in life.

A Call for Stronger Protections

Clean water should never be a luxury. It is a basic human need and a cornerstone of public health. Yet the combination of aging infrastructure, weak oversight, and unregulated chemicals has made safe water less certain. Protecting communities will require stronger laws, better monitoring, and a renewed commitment to ensuring that when we turn on the tap, we can trust what flows out.

Photography by Keenan Constance @keenangrams

Below are 15 toxins to keep an eye on for exposure: 

1. Arsenic: Used in a multitude of industrial processes, long-term exposure to inorganic arsenic through drinking water can lead to skin cancer, lung cancer, and bladder cancer. Arsenic is a confirmed carcinogen, and immediate poisoning can cause vomiting, abdominal pain, and diarrhea.

2. Cyanobacteria: Bacteria that comes from the rapid growth of blue-green algae and endangers drinking water supplies across the world. When ingested, cyanotoxins can attack the liver, create abdominal pain, vomiting, diarrhea, inflamed and bleeding liver, pneumonia, or kidney damage, and might even promote tumor growth. Some cyanobacteria produce unpleasant tastes and odors, which results in water treatment facilities increasing disinfectant byproducts.

3. Dioxins: Released during combustion, such as the burning of hazardous waste, forest fires, cigarette smoke, and burning oil and coal. Long-term exposure can affect the immune, nervous, endocrine, and reproductive system.

4. Disinfection Byproducts: Chemicals used in drinking water disinfection processes, such as chlorine, trihalomethanes, and haloacetic acids, are added to drinking water for purification, despite it not being completely safe. Chlorine is a reactive chemical and bonds with water, including the water in your gut. A mixture of these chemicals, forming byproducts, may damage cells and increase cancer risk.

5. Fluoride: A waste byproduct from the phosphate industry, fluoride, is an artificial chemical added to drinking water supplies to prevent tooth decay. Fluoride can collect in parts of the bone, which might affect the risk of osteosarcoma and can be an endocrine disruptor harming the thyroid gland. In June 2020, a federal lawsuit in California went to trial and could change the longstanding practice of adding fluoride to drinking water supplies.  

6. Lead: A heavy metal that can leach from lead pipes and plumbing fixtures. It can cause an increase in attention-related behavioral issues, stunted growth, autism, and neurological problems in children. Lead is toxic to almost every organ.

7. Mercury: Mercury vapor can linger in the atmosphere and ride the winds halfway around the globe. It can cause brain damage, cognitive disability, headaches, weakness, tremors, mood swings, memory loss, and skin rashes.

8. Nitrates: A widespread contaminant due to their use in fertilizer. It is a growing problem in many agricultural areas and places where there is sewage pollution from livestock manure and human sludge. Nitrate can be harmful to pregnant women and increase the risk of colon, kidney, and stomach cancer.

9. Pathogens: Bacteria, viruses, and parasites that cause diarrhea, vomiting, cramps, nausea, headaches, and fever can find a way into water supplies inadequately treated to kill germs.

10. PCBs: Polychlorinated biphenyls are chemicals used for industrial purposes such as insulation, oil, paints, adhesives, and fluorescent lights. PCBs were banned in 1979 but are still present in landfills. They break down slowly and infiltrate the environment. Ingestion of these chemicals can cause cancer, nervous, and endocrine system issues.

11. Perchlorate: Toxic chemicals used in rocket fuel, explosive road flairs, can interfere with thyroid hormone production. They dissolve and seep into groundwater from military and industrial sites.

12. Pesticides: Atrazine, DDT, glyphosate, HCB (hexachlorobenzene), and dacthal are some of the most commonly detected pesticide chemicals in water and soil. Some of these chemicals are persistent and can travel long distances in the atmosphere. Runoff from agricultural areas enters groundwater and contaminates wells. Epidemiological studies have reported associated damage to adrenal glands, kidneys, liver, thyroid, spleen, and cancer risk to these chemicals. 

13. PFAS: Per-and poly-fluoroalkyl substances are dangerous human-made chemicals that do not break down over time; they remain in the environment and our bloodstreams for decades. They are toxic to our health. Scientific studies show that PFAS may interfere with natural human hormones and the immune system, increase cholesterol, disrupt liver, thyroid, and pancreatic function, and increase cancer risk.

14. Radioactive contaminants: Radioactive material from the production of nuclear weapons, energy, and medicines can get in drinking supplies through leaks and improper waste storage. Exposure can cause cancer or kidney failure.

15.  Vinyl Chloride: Used to make PVC plastic products, vinyl chloride is a cancer-causing contaminant that can leach from older piping and has been found in drinking water.

Photo by Jon Mark Smith @mrrrk_smith

How to Know If Your Drinking Water Is Contaminated

The most reliable way to determine whether your drinking water is contaminated is through testing. At-home kits, available online or at most hardware stores, use strips that change color when they detect certain contaminants. While these kits provide a quick snapshot, a more thorough option is to hire a trained technician who can collect samples and send them to a certified laboratory for professional analysis.

If you are concerned about poor tap water quality, investing in a water filter is often a better choice than relying on bottled water. Bottled water not only generates massive amounts of plastic waste but is also frequently sourced from groundwater in unsustainable ways. When choosing a filtration system, look for products certified with the NSF mark, a trusted independent standard that ensures filters have been rigorously tested for effectiveness.

Understanding contamination levels can be complicated. The amount of water consumed varies from person to person, and some groups, like children, pregnant women, and people with compromised immune systems, are more vulnerable than others. While official drinking water standards exist, many harmful contaminants remain poorly studied or unregulated.

Prevention is critical. Protecting water sources means reducing pollution from sewage, fertilizers, pesticides, gasoline, and industrial waste. Communities should also stay alert to potential threats from new developments, manufacturing plants, or other industrial projects that may increase risks. If test results show contaminants exceeding health standards, consult local experts such as your health department, public water officials, or environmental geologists for guidance on next steps.

Staying hydrated is essential for health, but it’s equally important to minimize exposure to harmful chemicals. The more you understand about water quality, the better equipped you’ll be to make choices that protect both your family and your community.

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Additional Resources and Information: 

1. “A Water Utility Manager’s Guide to Cyanotoxins” American Water Works Association & Water Research Foundation: http://www.waterrf.org/PublicReportLibrary/4548a.pdf
2. American Cancer Society on Fluoride in Drinking Water: https://www.cancer.org/cancer/cancer-causes/water-fluoridation-and-cancer-risk.html
3. Atrazine and cancer risk: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C10&as_vis=1&q=atrazine+cancer+risk&btnG=
4. Center for Disease Control and Prevention (CDC) general information on HABs: http://www.cdc.gov/habs/
5. Dacthal and cancer risks: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C10&as_vis=1&q=dacthal+cancer+risk&btnG=
6. Environmental Protection Agency Drinking Water Requirements for States and Public Water Systems: https://www.epa.gov/dwreginfo/chemical-contaminant-rules
7. Environmental Protection Agency website on the effects of Harmful Algal Blooms: https://www.epa.gov/nutrientpollution/harmful-algal-blooms
8. Environmental Protection Agency website on Harmful Algal Blooms & Drinking Water: https://www.epa.gov/water-research/harmful-algal-blooms-drinking-water-treatment
9. Environmental Science & Technology Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: https://pubs.acs.org/doi/10.1021/acs.est.7b05440
10. Centers for Disease Control and Prevention Disinfection By-Products: https://www.cdc.gov/safewater/chlorination-byproducts.html
11. DDT and cancer risk: https://scholar.google.com/scholar?q=ddt+cancer+risk&hl=en&as_sdt=0&as_vis=1&oi=scholart
12. HCB (hexachlorobenzene) Cancer Risk: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C10&as_vis=1&q=HCB+cancer+risk&btnG=
13. Lead in U.S. Drinking Water: https://www.sciline.org/evidence-blog/lead-drinking-water
14. Microbial Contamination of Drinking Water and Human Health: https://link.springer.com/article/10.1007/s40572-014-0037-5
15. Monitoring Human Tissues for Toxic Substances: https://www.ncbi.nlm.nih.gov/books/NBK234183/
16. New England Bladder Cancer Study: https://dceg.cancer.gov/research/cancer-types/bladder/bladder-new-england
17. NSF website on Blue-Green Algae in Drinking Water: https://www.nsf.org/consumer-resources/water-quality/drinking-water/blue-green-algae-toxins-in-drinking-water
18. Toxic Chemicals: The Health Dangers of Chlorine: https://globalhealing.com/natural-health/toxic-chemical-health-dangers-chlorine/
19. Toxic Metal: The Health Dangers of Lead: https://globalhealing.com/natural-health/toxic-metal-health-dangers-lead/
20. U.S. Environmental Protection website on Cyanobacterial Harmful Algal Blooms: https://www.epa.gov/nutrient-policy-data/cyanohabs
21. World Health Organization Key Facts on Arsenic Exposure: https://www.who.int/news-room/fact-sheets/detail/arsenic