Millions of Americans drink tap water contaminated with harmful chemicals, but where does this pollution come from?
There’s no single source of water pollution. Industrial facilities, agriculture, aging infrastructure and wastewater are some of the most common sources of chemicals of concern and other problematic substances in tap water. This includes the “forever chemicals” known as PFAS, as well as arsenic, nitrates and more linked to a host of health harms.
Despite widespread contamination, the federal government gives most drinking water in the U.S. the passing grade of “legal.” But treated tap water with pollution levels below legal limits isn’t necessarily safe.
Utilities treat water to tackle many contaminants. They pull water from surface water – rivers, streams and lakes – and groundwater. This treatment can vary considerably.
The quality of treated raw, or source, water can be lower in heavily populated areas, where a lot of polluted runoff enters surface waterways such as creeks and rivers. Source water can also be inferior in places with lots of industry or agriculture.
And small systems that serve fewer people may not receive enough revenue from ratepayers to implement expensive cutting-edge treatment technologies.
Protection of water sources and watersheds from pollution is smart economics. Keeping contaminants out of water in the first place is more cost-effective for water providers than removing them year after year.
Yet most policy in the U.S. focuses on cleaning up contaminated water, rather than preventing pollution. Federal programs that allocate grants and low-cost loans to protect rivers, streams and groundwater from pollution don’t get the funding support they need.
Drinking water pollution sources
Increased federal funding could provide a vital boost to water systems of all sizes in targeting the many different sources of pollution across the U.S. These sources include:
Agriculture
Farming is one of the main sources of water pollution in American rivers, streams, lakes, wetlands and groundwater.
Every year, farmers apply more than 12 million tons of nitrogen fertilizer and 4 million tons of phosphorus fertilizer to cropland, at least some of which runs off into water sources.
Animal manure can also contaminate the water. As of 2023, U.S. livestock produce more than an estimated 1.4 billion tons of manure in the U.S. The manure doesn’t just stay on feedlots – it’s also applied to farm fields as fertilizer, often with commercial fertilizer.
That’s why runoff from farms and feedlots is typically loaded with disease-causing pathogens, as well as chemicals like nitrogen and phosphorus, and pesticides.
Many water utilities depend on expensive and complicated technologies, such as activated carbon treatment and ion exchange, to remove agricultural pollutants from water supplies.
Farm pollution doesn’t just contaminate the source water for rural consumers. It also creates an expensive problem for many cities. A 2020 EWG analysis found that the tap water for 60 million city dwellers contains elevated levels of nitrate. And those results are for treated water; nitrate levels in source water are even higher.
Pollution from farms and factory farms is almost completely exempt from water pollution laws, including the Clean Water Act that was enacted more than 50 years ago.
Manufacturing and businesses
In 2022, U.S. industries and businesses discharged 198 million pounds of chemicals into rivers and streams, according to the EPA’s Toxics Release Inventory reporting program. Many of these waterways serve as sources of drinking water and may contain concerning levels of several contaminants.
Water utilities regularly detect hundreds of industrial chemicals in finished, or treated, tap water. Many of these chemicals can legally be present in drinking water at any concentration, because federal and state authorities do not limit them.
The unregulated contaminant 1,4 dioxane can contaminate groundwater from legacy EPA-designated Superfund cleanup sites contaminated with industrial solvents. Production of the plastic polyethylene terephthalate can also release the pollutant into surface waters.
Hexavalent chromium from industrial processes can contaminate groundwater from environmental releases. These sources include wastewater from electroplating facilities, manufacturing and cement production.
Trichloroethylene is used as a solvent to clean metal parts and other uses in the semiconductor industry, in turn contaminating U.S. groundwater.
Military bases and airports
The Department of Defense’s many facilities are known to be a major source of PFAS water contamination in the U.S., primarily through the military’s use of firefighting foam that contains PFAS. Many commercial service airports also use the foam, making them another PFAS contamination source.
EWG has mapped at least 720 military sites either known or suspected sources of discharging PFAS, which ends up in drinking water. These sites can be found in all 50 states, the District of Columbia and Puerto Rico.
Wastewater and stormwater runoff
Wastewater contains contaminants such as antibiotic-resistant bacteria, PFAS, personal care products and residues from prescription drugs like birth control pills and illegal drugs.
And standard treatment processes at wastewater plants don’t eliminate these substances.
Stormwater runoff is laced with chemicals from vehicle emissions, road surfaces, yards and homes. In most places, it enters waterways without being treated. The runoff contaminates rivers and streams and therefore drinking water sources with gasoline additives, microplastics, household pesticides and other chemicals known to cause health problems.
As the U.S. population grows, and more land is swallowed up by manufacturing and other industrial uses, roads, urban sprawl and agriculture, the number of contaminants polluting lakes and rivers from runoff will increase, which may result in more tap water pollution.
Water infrastructure and treatment
Water pipes, tanks and other types of infrastructure throughout the U.S. are aging. In many places, contaminants can corrode from infrastructure into the water supply. Lead and copper can leach from pipes into water, as can chemicals from plastic piping.
The EPA estimates a need for more than $625 billion over the next 20 years to improve water infrastructure to meet public health demands. While much of this funding is needed for basic rebuilding of the deteriorating U.S. water system, that work will also significantly reduce contaminants leaching into supplies.
Disinfecting drinking water is necessary, but can also cause contamination. Utilities and other systems use chlorine or other chemicals to treat water to kill disease-causing pathogens. But when disinfected, the process can produce toxic byproducts if the water contains organic matter such as soil, fertilizer and animal waste.
Scientists have identified more than 600 disinfection byproducts in treated drinking water, and some of the most common are linked to DNA damage and cancer. Reducing organic matter in drinking water can lower the formation of disinfection byproducts.
Naturally occuring contamination
Not all water contamination is caused by human activity – some occurs naturally.
Radioactive chemicals, metals and other elements are natural components of soil and rocks that may dissolve into rivers, streams and groundwater sources. Many of these contaminants are known to harm health.
But contamination can rise above these naturally occurring levels as a result of mining operations, agriculture and building construction, among other activities.
February 2025