The Power of Information

National Drinking Water Database

National Drinking Water Database - Pollution Sources

Drinking water pollution has many sources

December 2009

Tap water contaminants found in EWG's study include a wide range of compounds, including agricultural chemicals, effluents from industrial and municipal wastewater facilities, water treatment and distribution byproducts, urban runoff and naturally occurring substances whose levels rise as a result of suburban sprawl and deforestation. Whatever the sources of water pollution, these contaminants pose potential health risks to the public, especially infants and children and other vulnerable populations.

bar chart: chemicals detected by category

Table 3. Many Americans have gotten water with contaminants above health-based guidelines

Source of pollutant Number detected Number of states where detected Total number of people exposed Number of people exposed over health-based guidelines*
Total chemical contaminants found 315 45 256,000,000 252,000,000
Agricultural see all 97 46 215,664,000 127,498,258
Industrial see all 204 46 241,437,000 204,950,207
Sprawl and urban areas see all 86 46 236,933,000 177,124,541
Water treatment, storage, and distribution see all 42 45 240,744,000 235,606,510
Naturally Occuring 48 46 239,961,000 198,613,659

Source: EWG analysis of water utility test data for 2004-2009, compiled and provided to EWG by state drinking water offices. Some pollutants stem from multiple sources and are included in all relevant categories.

*Health-based guidelines included in this analysis include enforceable drinking water standards (Maximum Contaminant Levels or MCLs) as well as governmental, non-enforceable health guidelines, such as Maximum Contaminant Level Goals (MCLGs), lifetime health advisory levels, one-day and ten-day advisory levels to protect children from non-cancer health endpoints, and other government-established health guidelines for tap water contaminants.


Agricultural activities are the largest source of water pollution in rivers and streams around the country (EPA 2008f; EPA 2009r). EWG's analysis of utilities' tap water test results found that water contaminated by 97 agricultural pollutants, including pesticides and fertilizer ingredients, has been supplied to 215,664,000 people in 46 states. 61% of those people have gotten water containing one or more agricultural contaminants present at levels above health-based limits recommended in government advisories.

Nearly two-thirds (62) of the agricultural chemicals detected in tap water are unregulated, with no legally mandated limit.

According to U.S. Department of Agriculture figures, agriculture spreads commercial fertilizer over one-eighth of the continental U.S. land mass every year (AAPFCO 2002; USDA 2009). In 2007, the latest year for which USDA statistics are available, more than 100 billion pounds of fertilizer were applied over 266 million acres (USDA 2009). Herbicides are spread over one-tenth of the lower 48 states (USDA 2009).

In addition, EPA estimates that there are 238,000 concentrated feed lots for cattle and pigs - the equivalent of 75 in every county - that collectively produce 500 million tons of manure yearly (EPA 2005c).

Runoff from farms and feed lots can be laden with sediments, disease-causing microorganisms, pesticides and fertilizer ingredients that contaminate water supplies (EPA 2009r). Despite this, EPA has failed to set pollution prevention standards for agricultural operations as mandated under the Clean Water Act. That forces water suppliers to treat water supplies to remove pesticides and related pollutants, often relying on additional processes such as carbon treatment at a cost to taxpayers running into millions of dollars. Despite such treatment, millions of Americans drink water containing the residues that remain.


EWG's analysis found that water contaminated with 204 industrial pollutants, including plasticizers, solvents, and propellants, has been provided to 241,437,000 people in 46 states. Of them, 85% got water containing one or more industrial contaminants present at levels above health-based limits recommended by government advisories.

More than half (126) of the industrial chemicals detected in tap water are unregulated, with no legally mandated limit.

The EPA has registered approximately 83,000 chemicals for use in the U.S.; about 3,000 of them are manufactured and/or imported in amounts exceeding 1 million pounds a year (GAO 2005a; EPA 2008d). The EPA approves an average of two new industrial chemicals every day, 80 percent them within three weeks of an industry application, with or without safety studies (GAO 2005b; EPA 1998b). A 1998 EPA study found that fully 43 percent of chemicals used in the highest volumes (more than 1 million pounds per year) lacked any of the seven most basic health and safety screening studies, let alone substantive information on their potential to pollute tap water sources (EPA 1998e).

Health officials do not know the full extent of industrial pollution of drinking water supplies or the health consequences of exposures. But they do know with certainty that some of these chemicals end up in rivers, streams, reservoirs and groundwaters that provide drinking water, and that many persist all the way to the tap. EPA's Toxics Release Inventory reporting program shows that in 2007, the latest year for which national statistics are available, U.S. industries discharged 232 million pounds of 244 chemicals into rivers and streams (EPA 2009i). Most of these industrial chemicals remain untested and unregulated in tap water.

Runoff from urban areas and suburban sprawl

The number of contaminants polluting lakes and rivers increases as more land is cleared for homes and agriculture, according to a U.S. Geological Survey study of nine watersheds across the country (Kingsbury 2008), inevitably resulting in tap water pollution. EWG's analysis found that water contaminated with 86 pollutants linked to sprawl and urban areas, including road runoff, lawn pesticides, and wastewater chemicals, has been provided to 236,933,000 people in 46 states. 76% of those people were served water with one or more of these contaminants present at levels above government health guidelines.

56 of the urban and sprawl runoff chemicals detected in tap water are are unregulated, with no legally mandated limit.

As the U.S. population continues to grow, water supplies are strained by increasing loads of wastewater and storm water runoff laden with the signature pollutants of urban areas and suburban sprawl - chemicals from automobile emissions, road surfaces, yards and homes, and from wastewater treatment plants that dump effluent into waterways at a rate of 60 gallons per person every day.

While growth benefits the economy, in the absence of national, state or local plans that recognize - and control - impacts on the environment, growth strains streams and rivers and burdens water suppliers with ever-increasing loads of pollutants. Government studies show that each new member of the population spurs housing, business and infrastructure development that consumes an average of slightly more than one acre of countryside (U.S. Census Bureau 2009; U.S. Global Change Research Program 2004). At the current growth rate of nearly three million people each year, this translates every year into tainted runoff from new development that would cover an area one and a half times the size of Yellowstone National Park. It also adds 66 billion gallons of wastewater to U.S. waterways.

Development degrades water supplies in unexpected ways. Scientists are finding that rivers, streams and drinking water are contaminated with antidepressant and anticonvulsive medications; antimicrobial hand soap and toothpaste chemicals such as triclosan and triclocarban; active ingredients in oral contraceptives and thyroid hormone treatments; fragrance compounds; flame retardants; plasticizers such as Bisphenol A; and hormone-mimicking detergents (Associated Press 2008; Barnes 2008; Batt 2008; Benotti 2009; Focazio 2008; Kingsbury 2008; Young 2008). The list of unregulated wastewater-related compounds detected in source and tap water includes 108 chemicals, and this number is expected to grow as the population increases.

Pharmaceuticals and personal care product chemicals are excreted in human urine or washed down the drain. Many are not eliminated by standard treatment processes at wastewater treatment plants. A landmark study released by the USGS in 2008 found that many of these chemicals also resist removal at tap water treatment plants (Kingsbury 2008).

Findings of pharmaceuticals and personal care product chemicals in drinking water across the entire U.S. reveal severe deficiencies in current safety standards:

The presence of pharmaceuticals and personal care product chemicals in drinking water reveals severe deficiencies in current safety standards:

[S]tandards or advisories have not been established for most of these compounds... Drinking-water criteria currently are based on the toxicity of individual compounds and not combinations of compounds. Little is known about potential human-health effects associated with chronic exposure to trace levels of multiple OWCs [organic wastewater-related contaminants] through routes such as drinking water. The occurrence in drinking-water supplies of many of the OWCs analyzed for during this study is unregulated and most of these compounds have not been routinely monitored for in the Nation's source- or potable-water supplies" (Stackelberg 2004).

Without a national, coordinated initiative to control pollution from population growth and sprawl and to modernize health protections for drinking water exposures, municipal water users can expect ever-growing loads of these pollutants and elevated risks to human health.

Water treatment, storage, and distribution

EWG's analysis found that water contaminated with 42 pollutants that are residues of water treatment, storage, and distribution, including chemical byproducts of water disinfection, has been supplied to 240,744,000 people in 45 states and the District of Columbia. 97% of those people got water with one or more of these contaminants present at levels above health-based limits recommended in government advisories.

24 of these chemicals detected in tap water are are unregulated, with no legally mandated limit.

Water disinfection is considered one of the great public health triumphs of the 20th century, but 100 years after its inception consumers of tap water still face health risks due to disinfection byproducts. Water utilities add disinfectants to the water to reduce the risk of infectious disease from microbes, but these chemicals can increase the risk of cancer risks and problems in development and reproduction.

The chemicals can form harmful byproducts when they react with organic pollution from agriculture and runoff from urban areas and suburban sprawl. EPA restricts the levels of 11 chemicals that have been linked to DNA damage and cancer, but scientists have identified more than 600 disinfection byproducts in treated drinking water (Chowdhury 2009; Krasner 2006, 2009; Richardson 1998, 1999a,b, 2003, 2007). EPA has required short-term testing for only a handful in unregulated contaminant monitoring programs: EWG's analysis of water utilities' 2004-2009 tests of tap water quality revealed 19 unregulated disinfection byproducts altogether, in water consumed by 61.1 million Americans in 4,984 communities.

Federal clampdowns on nine regulated byproducts (four chemicals known as trihalomethanes and five haloacetic acids) have spurred changes in water disinfection regimes at plants across the country. Many water systems switched from chlorine to alternative chemicals or mixtures of disinfectants and, as a result, generated novel, largely unstudied suites of disinfection byproducts.

Potential risks from water treatment chemicals don't end with disinfection. Water tanks and pipes in the distribution system - including pipes in the home - also add a significant load of pollutants. Lead from pipes and lead-based solder can leach into water (Edwards 2009; Maas 2007; Zhang 2009). Asphalt- or coal tar-lined storage tanks and pipes can leach chemicals linked to cancer, called polycyclic aromatic hydrocarbons (PAHs) (World Health Organization 2004a). Critical upgrades to pipes, tanks and other aging treatment and distribution facilities are a part of water utilities' $334.8 billion need for infrastructure investments over the next 20 years (EPA 2009p).

Rivers, streams, and lakes are severely polluted

EWG's investigation reveals major gaps in the system of public health protections for drinking water. Federal programs that allocate grants and low-cost loans to prevent water pollution and protect the rivers, streams, and groundwater that Americans drink from are sorely underfunded.

Just 4 percent of $68 billion granted to states under the Clean Water State Revolving Fund during the 1987-2009 period went toward mitigating polluted runoff from farms and urban areas, which accounts for 60 percent of water pollution (EPA 2009n). And only $12.7 million has been allocated to conserve buffer zones along rivers and streams under the Drinking Water State Revolving Fund over its entire 13-year history (1997-2009) (EPA 2009l; EPA 2009m).

In its most recent national Water Quality Inventory Report to Congress for 2006-2008, EPA found that 66 percent of lakes and 50 percent of streams and rivers were "impaired" - unsafe for drinking, fishing or even swimming, in some cases (EPA 2009r). By failing to clean up rivers and reservoirs that provide drinking water for hundreds of millions of Americans, EPA and the Congress have forced water utilities to decontaminate water polluted by industrial chemicals, factory farm waste, sewage, pesticides, fertilizers and sediment.

Even after water suppliers filter and disinfect the water, scores of contaminants remain, as conventional treatment regimes remove less than 20 percent of some contaminants (Faust 1998). By failing to set tap water safety standards expeditiously or require and fund comprehensive testing, EPA allows widespread exposures to chemical mixtures that pose largely unknown risks to human health.