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Nitrate in Drinking Water, 2003-2017: Pennsylvania

Between 2003 and 2017, tests detected elevated levels of nitrate (3 milligrams per liter, or mg/L) in the tap water supplies of 647 towns and cities in Pennsylvania, serving approximately 6 million people.

Contamination is getting worse in 266 of those community water systems1 – 41 percent, serving approximately 659,000 people. Larger towns and cities tend to depend on surface water for drinking, whereas small, often rural communities depend on groundwater. In Pennsylvania, just under 470,000 residents of 30 towns and cities that rely on surface water faced increased contamination. But 236 mostly small, rural communities, serving approximately 191,000 people, that depend on groundwater saw nitrate contamination increase.

Pennsylvania Communities With Increases in Nitrate Contamination, 2003 to 2017
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Source: EWG, from Pennsylvania Department of Environmental Protection data.

Average nitrate contamination across these communities jumped by 37 percent between 2003 and 2017. In 2003, average contamination was 3.62 mg/L. By 2009, average contamination had increased to 4.51 mg/L and continued climbing to 5.18 mg/L in 2017.

Average Nitrate Levels in Pennsylvania Communities Where Contamination Rose, 2003 to 2017

Source: EWG, from Pennsylvania Department of Environmental Protection data.

Health Hazards of Nitrate

Nitrate is a primary chemical component of fertilizer and manure that can run off farm fields and seep into drinking water supplies. Under the federal Safe Drinking Water Act, the legal limit for nitrate, measured as nitrogen, in drinking water is 10 mg/L. This limit was set in 1962 to guard against so-called blue baby syndrome, a potentially fatal condition that starves infants of oxygen if they ingest too much nitrate.

But more recent studies show strong evidence of an increased risk of colorectal cancer, thyroid disease and neural tube birth defects at levels at 5 mg/L or even lower. During the period studied, drinking water was getting worse in 151 Pennsylvania communities, serving approximately 307,000 people, that already had tested at or above 5 mg/L at least once between 2003 and 2017.

Drinking water for approximately 51,000 of those people in 34 communities had already tested at or above the legal limit at least once and had increasing nitrate levels during the period studied. Of the 99 communities where nitrate exceeded the Environmental Protection Agency’s legal limit at least once, 16 systems, serving approximately 18,862 people, tested at or above the legal limit in 2017.

People who want to know the level of nitrate in their community’s water system can visit the Pennsylvania page of EWG’s Tap Water Database.

Who Is Affected?

Contamination was more likely to get worse in smaller communities between 2003 and 2017. Eighty-eight percent of systems where contamination increased served 3,300 or fewer people. For our analysis, systems were put into the EPA-designated size categories based on how many water customers they serve.

Number and Percent of Systems With Increasing Nitrate Levels, by System Size, 2003 to 2017

System size System count Percent of systems
Very small (<501) 170 64%
Small (501-3,300) 63 24%
Medium (3,301-10,000) 20 8%
Large (10,001-100,000) 12 5%
Very large (>100,000) 1 0%

Source: EWG, from Pennsylvania Department of Environmental Protection data.

Pennsylvania was one of three states where nitrate contamination was more likely to get worse in urban than in rural communities. In Pennsylvania, 46 percent of communities with growing nitrate levels were rural, whereas 54 percent were urban, as defined by the U.S. Census Bureau.


1 Community water systems are public water supplies that serve residents in cities and towns year-round.

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