EWG Investigation: Across Farm Country, Nitrate Pollution of Drinking Water for More Than 20 Million Americans Is Getting Worse

By Anne Weir Schechinger, Senior Analyst, Economics

WEDNESDAY, JUNE 24, 2020

In much of America’s farm country, nitrate contamination of drinking water, largely caused by polluted runoff from crop fields, poses a serious health risk – and the problem is getting worse, according to an Environmental Working Group analysis of data from 10 states.

Our investigation found that in the water of more than 2,100 utilities with the most serious problems, nitrate contamination has grown steadily worse. These community water systems1 serve almost 21 million people across vast stretches of the Midwest, Southwest, Atlantic Coast and California.

Data obtained under public records laws shows that between 2003 and 2017, tests detected elevated levels of nitrate in the tap water supplies of more than 4,000 community water systems in the states with the most widespread contamination – California, Illinois, Iowa, Kansas, Maryland, Nebraska, Oklahoma, Pennsylvania, Texas and Wisconsin.

Those water systems supply tap water for more than 45 million Americans. Each of the systems was contaminated with nitrate at or above 3 milligrams per liter, or mg/L, at least once in those 15 years. The Environmental Protection Agency considers 3 mg/L in groundwater used for drinking water an indication of contamination above naturally occurring levels.2

In 52 percent of those communities, serving 20.7 million people, nitrate contamination is getting worse. In California, Kansas and Texas, it’s getting worse in almost 60 percent of the communities with elevated nitrate levels.

This interactive map shows the systems that had at least one nitrate test at or above 3 mg/L between 2003 and 2017 and whose contamination levels went up during that period. Clicking on a state links to a more detailed interactive map for that state, with information about each system.



In Thousands of Communities, Nitrate Contamination of Drinking Water Is Getting Worse
Explore the Map

Source: EWG, from state data obtained under open records laws.

EWG’s analysis underscores what we reported in a study and map released in October 2019. The earlier analysis found that two-year average nitrate contamination, from 2016 and 2017, in almost 1,700 towns and cities were at or above the level that a meta-analysis found increases the risk of colon, kidney, ovarian and bladder cancers.

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. Although nitrate pollution can also come from wastewater treatment plants and septic systems, fertilizer and manure are the main culprits in agriculture-heavy regions.

Under the federal Safe Drinking Water Act, the legal limit for nitrate 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 have shown strong evidence of an increased risk of colorectal cancer, thyroid disease and neural tube birth defects at levels of 5 mg/L or even lower. People who are concerned about nitrate in their tap water can look up their water system in EWG’s Tap Water Database.

Eighty-six percent of the communities with elevated levels of nitrate rely on groundwater for their drinking water. Our analysis found that contamination is not only getting worse in places with nitrate tests above 3 mg/L – it’s also getting worse in many places that exceeded the EPA’s legal limit, or the lower level linked to cancer and other health effects.

Who Is Affected?

In the period studied, the smallest communities were more likely to have worsening contamination. Eighty percent of systems with worsening nitrate contamination served 3,300 or fewer people. For all states except California, two-thirds of communities with growing nitrate levels were in a rural area, rather than an urban area, as defined by the U.S. Census Bureau.

California is a special case, because so much of the state’s farming is located in what’s known as the urban-agricultural interface, with vast crop acreage inside urban areas. For example, Fresno, a city of more than 500,000 people, is surrounded by 1.88 million acres of cropland in Fresno County, the nation’s most productive agricultural county. Our analysis found that 71 percent of California communities with worsening nitrate contamination were in urban areas. For more detail, see the California profile.

In the table below, systems are categorized according to the EPA’s community size classifications.


Eighty Percent of Communities Where Nitrate Contamination Rose Were Small or Very Small

System size System count Percent of systems
Very small (<501) 1,114 53%
Small (501-3,300) 577 27%
Medium (3,301-10,000) 188 9%
Large (10,001-100,000) 196 9%
Very large (>100,000) 36 2%

Source: EWG, from state data and EPA community size classifications.

Removing nitrate from tap water is expensive. A city can spread the cost of treatment over a large customer base. But in small communities, the increased cost of treatment per person could be hundreds or even thousands of dollars a year, depending on the technology used. For more information on the potential cost of nitrate treatment, see this EWG report.

State-by-State Results

Details for each state are available in the state profiles found here:

California
Illinois
Iowa
Kansas
Maryland
Nebraska
Oklahoma
Pennsylvania
Texas
Wisconsin

To see the methods used in this study and detailed results, click here.



Notes

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

2 U.S. EPA, Estimated Nitrate Concentrations in Groundwater Used for Drinking. “While nitrate does occur naturally in groundwater, concentrations greater than 3 mg/L generally indicate contamination (Madison and Brunett, 1985), and a more recent nationwide study found that concentrations over 1 mg/L nitrate indicate human activity” (Dubrovsky et al. 2010).



Methodology

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Methodology and Detailed Results: In Farm Country, Nitrate Pollution of Drinking Water Is Getting Worse


By Anne Schechinger, Senior Analyst, Economics

WEDNESDAY, JUNE 24, 2020

In 2019’s Trouble in Farm Country Revisited[1] report, the Environmental Working Group reported that nitrate contamination of drinking water was rampant in 11 states – California, Illinois, Iowa, Kansas, Maryland, Minnesota, Nebraska, Oklahoma, Pennsylvania, Texas and Wisconsin. In March 2020, we found that more than 200,000 people in Minnesota were drinking water with nitrate contamination that got worse between 1995 and 2018.[2] Now new research from EWG shows that nitrate levels in community drinking water have also been increasing in the other 10 states over the past 15 years.

Between 2003 and 2017, tests detected elevated levels of the chemical in the tap water supplies of 4,037 community water systems serving almost 45.5 million residents in California, Illinois, Iowa, Kansas, Maryland, Nebraska, Oklahoma, Pennsylvania, Texas and Wisconsin. Contamination is getting worse in 52 percent, or 2,111, of these communities.

This increasing contamination does not just affect groundwater systems. Contamination in both groundwater and surface water systems is getting worse. And although there are not enough data to evaluate whether nitrate levels are getting worse in private wells over time, it is likely that nitrate levels are increasing in wells that households use for drinking, because they often draw water from the same sources as groundwater community water systems.

Nitrate is a chemical component of fertilizer and manure. It gets into groundwater and surface water sources of drinking water by running off farm fields and seeping into groundwater.

Drinking water with nitrate can have serious health consequences. Under the federal Clean Water Act, the legal limit for nitrate (measured as nitrogen) in drinking water is 10 milligrams per liter, or 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.[3] But newer research indicates that drinking water with 5 mg/L of nitrate or even lower is associated with higher risks of colorectal cancer and adverse birth outcomes, such as neural tube birth defects.[4]

How We Conducted the Study

The data for nitrate testing of drinking water came from the 10 states’ government agencies that record data from required tests of public water systems. For example, we received Iowa’s data from the Iowa Department of Natural Resources and California’s data from the California State Water Resources Control Board. Through public records requests, we received all finished water nitrate tests conducted at each community water system in each state between 2003 and 2017, except for Oklahoma, for which we received nitrate tests for 2007 to 2017 only. Many of these test results can be found in EWG’s Tap Water Database.[5] We chose 2003 as the earliest date in our analysis for nine of the states, because all had nitrate testing data going back to 2003.

We analyzed the data for all community water systems that the Environmental Protection Agency considered active as of April 2019 and that conducted at least one test for nitrate between 2003 and 2017 for the nine states, and 2007 and 2017 for Oklahoma. We analyzed nitrate tests that had an EPA Safe Drinking Water Information System contamination code of 1040 for California, Illinois, Iowa, Kansas, Maryland, Pennsylvania, Texas and Wisconsin but used contamination code 1038 for Nebraska and Oklahoma.[6] The dataset included systems that use either groundwater or surface water as their main source of drinking water.

Public water systems are either community or non-community systems. Community water systems typically serve residents in cities and towns year-round – they are what most people think of as municipal systems or water utilities. Non-community systems serve sites like churches and schools with their own source of drinking water, and serve much smaller populations, usually for only part of the year. In this analysis we studied community water systems only, since they serve considerably more people than non-community systems.

We then narrowed the list of active community water systems that tested for nitrate to those with elevated nitrate. A system was considered to have elevated nitrate if it had at least one test at or above 3 mg/L at any time between 2003 and 2017. The level of 3 mg/L was chosen to represent elevated nitrate because the EPA considers 3 mg/L in groundwater used for drinking water an indication of contamination above naturally occurring levels.[7]

For some of the analysis, we also looked at how many systems had at least one test at or above 5 or 10 mg/L, since 10 mg/L is the legal limit of nitrate in public drinking water, and 5 mg/L is associated with negative health outcomes. We took out all exceptionally high nitrate tests that were above 100 mg/L, since we deemed these to be errors and not actual test results.

Once we established the group of community water systems with elevated nitrate – those with at least one test at or above 3 mg/L – we analyzed whether their nitrate tests increased, decreased or stayed the same between 2003 and 2017 (between 2007 and 2017 in Oklahoma). This was done by evaluating whether nitrate tests were correlated with year.

For each community water system, a correlation coefficient, or value, was calculated to see whether nitrate positively or negatively correlated with year. Correlation coefficients describe the relationship between the two variables: Positive r values that are close to +1 show a strong relationship between year and increasing nitrate, and negative values close to -1 show a strong relationship between year and decreasing nitrate.

Nitrate levels had increased in those community water systems that had a positive correlation, an value above zero. Nitrate levels had decreased in systems with a negative correlation, an value below zero. A few systems had zero correlation, which means their nitrate levels neither increased nor decreased over time. The summary report focuses on all systems with a positive correlation.

After finding the correlation coefficients for every system with elevated nitrate, we calculated the t and values for each system.[8] These indicators determine whether the increase or decrease in nitrate over time was statistically significant. If the correlations at each system were statistically significant, that meant the increase or decrease in nitrate was not just a random increase or decrease.[9] We evaluated statistical significance at a 95 percent confidence level (p<=0.05).

Besides studying whether each community water system’s nitrate levels increased or decreased between 2003 and 2017, we also looked at whether the overall annual nitrate average across all elevated systems went up over time. (Test results reported as “non-detects” were assigned a value of zero.) We did this by calculating the average of annual tests for all systems with elevated nitrate between 2003 and 2017 by state, and then the growth rate in nitrate averages from year to year. The average across all the years’ growth rates provided the annual average growth rate for all elevated systems in each state, which was the average increase in the nitrate average in one year. The sum of all the annual growth rates in nitrate averages across the time period gave the overall growth rate in nitrate levels from 2003 to 2017, by state.

Contamination in smaller community water systems was more likely to get worse between 2003 and 2017. To figure out whether more systems with increasing nitrate levels over time were small or large, systems were put into EPA-designated size categories based on how many water customers each system served.[10] Very small community water systems serve 501 people or fewer; small systems serve between 501 and 3,300; medium systems between 3,301 and 10,000; large systems between 10,001 and 100,000; and very large systems serve over 100,000 people.

People in rural areas are also more likely to experience worsening nitrate contamination. To determine  this, we put the location of each community system onto a map with 2010 U.S. Census Bureau–designated urban areas. The census delineates an “urban area” as one of two things, “urbanized areas (UAs) that contain 50,000 or more people and urban clusters (UCs) that contain at least 2,500 people.”[11] If a community water system was located in a U.S. Census Bureau–designated urban area, it was considered an urban system, and if not, it was considered a rural system.

Detailed Results

Between 2003 and 2013, 14,276 community water systems that provided water for approximately 104 million people in California, Illinois, Iowa, Kansas, Maryland, Nebraska, Oklahoma, Pennsylvania, Texas and Wisconsin tested their finished drinking water for nitrate at least once. (The population listed for the systems was 104,395,379, but population listed for community water systems can be imprecise.) Of those, 28 percent had at least one test at or above 3 mg/L; 19 percent had at least one test at or above 5 mg/L; and 7 percent had at least one test at or above 10 mg/L (Table 1).

Table 1. Percent of Active Community Water Systems That Had at Least 1 Test at or Above 3, 5 or 10 mg/L, by State

State

Percent of systems with at least 1 test >=3 mg/L

Percent of systems with at least 1 test >=5 mg/L

Percent of systems with at least 1 test >=10 mg/L

California

44%

31%

12%

Illinois

18%

13%

3%

Iowa

27%

19%

5%

Kansas

61%

46%

17%

Maryland

32%

19%

5%

Nebraska

65%

53%

26%

Oklahoma

38%

27%

12%

Pennsylvania

36%

23%

5%

Texas

8%

5%

2%

Wisconsin

30%

18%

5%

Total

28%

19%

7%

For systems with at least one test at or above 3 mg/L, 52 percent, or 2,111 community water systems, had increasing nitrate levels over time. California, Kansas and Texas had the highest percentage of communities with worsening nitrate contamination at 57 percent (Table 2).

Table 2. Community Water Systems With at Least 1 Test at or Above 3 mg/L That Had Increasing or Decreasing Nitrate Over Time, by State

State

Number of increasing systems

Percent of increasing systems

Number of decreasing systems

Percent of decreasing systems

California

669

57%

503

43%

Illinois

118

54%

95

44%

Iowa

126

53%

106

45%

Kansas

203

57%

154

43%

Maryland

77

54%

                                                       66

46%

Nebraska

159

46%

                                                    187

54%

Oklahoma

110

50%

                                                    107

49%

Pennsylvania

266

41%

                                                    379

59%

Texas

218

57%

                                                    165

43%

Wisconsin

165

54%

                                                    136

45%

Total

2,111

52%

                                               1,898

47%

Of the systems with increasing levels of nitrate contamination, 45 percent were statistically significant. However, of the 47 percent of systems where nitrate levels went down over time, only 41 percent decreased significantly. At 55 percent, California had the highest percentage of systems with increasing contamination that was statistically significant (Table 3).

Table 3. Community Water Systems With at Least One Test at or Above 3 mg/L That Had Statistically Significant Increases or Decreases in Nitrate, by State

State

Number of systems with increase

Percent of systems with increase

Number of systems with decrease

Percent of systems with decrease

California

370

55%

235

47%

Illinois

35

30%

28

29%

Iowa

58

46%

50

47%

Kansas

97

48%

51

33%

Maryland

29

38%

18

27%

Nebraska

83

52%

88

47%

Oklahoma

30

27%

30

28%

Pennsylvania

100

38%

176

46%

Texas

93

43%

61

37%

Wisconsin

64

39%

42

31%

Total

959

45%

779

41%

Figure 1 provides the annual nitrate averages by state between 2003 and 2017 for all systems with elevated nitrate contamination – at least one test at or above 3 mg/L – that had worsening nitrate over time. Oklahoma’s annual nitrate averages were only between 2007 and 2017.

Figure 1. Average Annual Nitrate for Community Water Systems With Increasing Nitrate Between 2003 and 2017, by State

When looking at average nitrate levels for communities with worsening nitrate, Wisconsin had the largest increase in nitrate between 2003 and 2017 at 46 percent. Kansas had the smallest growth rate over those years, but its nitrate averages grew 17 percent in that time nonetheless (Table 4).

Table 4. Growth Rate in Nitrate Averages Between 2003 and 2017 for the Community Water Systems With Increasing Nitrate, by State

State

Percent increase in nitrate averages between 2003 and 2017

California

31%

Illinois

43%

Iowa

29%

Kansas

17%

Maryland

26%

Nebraska

28%

Oklahoma

44%

Pennsylvania

37%

Texas

21%

Wisconsin

46%

Nitrate contamination is more likely to get worse for people living in rural areas. At 86 percent, Nebraska had the highest percentage of increasing nitrate systems located in a rural area (Table 5).

Table 5. Percent of Increasing Nitrate Community Water Systems Located in a Rural Versus Urban Area, By State

State

Percent rural

Percent urban

California

37%

63%

Illinois

62%

38%

Iowa

73%

27%

Kansas

79%

21%

Maryland

34%

66%

Nebraska

86%

14%

Oklahoma

79%

21%

Pennsylvania

46%

54%

Texas

69%

31%

Wisconsin

65%

35%

Total

57%

43%


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