Nitrate contaminates drinking water for almost 60 million people in cities across the country
UPDATED: November 3, 2021
By Anne Schechinger, EWG Senior Analyst of Economics
Drinking water supplies for almost 60 million people living in major cities and other urban areas throughout the U.S. are contaminated with elevated levels of nitrate, according to a new EWG analysis. Nitrate is a pollutant linked to cancer and potentially dangerous for infants.
Since nitrate in drinking water is commonly caused by agriculture, it is widely considered to be a rural, small-town issue. EWG’s Trouble in Farm Country report, updated in 2019, highlighted the risks such communities face. Our 10-state nitrate investigation in 2020 detailed how the threat of nitrate in drinking water is getting worse for at least 20 million people across 10 states.
But EWG’s new findings show that nitrate pollution is also an issue facing big cities like Los Angeles and Las Vegas and smaller cities. In some cases, nitrate levels exceed the legal limit.
At least 22.7 million of the people affected live in California. After California, the three states with the most residents drinking nitrate-contaminated water are Arizona, with almost 5.2 million people; Pennsylvania, with more than 4.5 million people; and New Jersey, with 3.2 million people.
Nitrate is a chemical component of fertilizer and animal manure that can run off farm fields and get into both surface water and groundwater sources of drinking water. It can get into drinking water supplies via urban runoff and municipal wastewater discharges, but agricultural runoff is the main source of contamination in many states.
Our latest analysis expands the focus to show that almost 60 million people in cities across the U.S. are at risk.
The analysis finds that 59.5 million people get drinking water from 757 large or very large community water systems that had at least one detection of nitrate at or above 3 milligrams per liter, or mg/L, between 2017 and 2019. The analysis used EWG’s newly updated Tap Water Database to arrive at these findings.
The federal legal limit for nitrate in drinking water is 10 mg/L, as established by the Environmental Protection Agency. This limit was based on a 1962 U.S. Public Health Service recommendation designed to guard against blue baby syndrome, a potentially fatal condition that starves infants of oxygen if they ingest too much nitrate.
But recent studies show strong evidence of an increased risk of colorectal cancer, thyroid disease and neural tube birth defects at 5 mg/L and other levels far below the legal limit.
The EPA nominated nitrate to receive a new health assessment through the Six Year Review process in 2010, to evaluate whether the limit allowed in tap water should be changed. An initial plan for the assessment was released in 2017, but the Trump administration canceled that review in 2019.
Nitrate in large and very large drinking water systems
Nitrate is widespread in community water systems, which are public water systems that serve at least 25 people year-round. The EPA considers any water system to be “large” if it serves between 10,001 and 100,000 people, and “very large” systems serve more than 100,000 people.
Table 1 shows that of the 757 large or very large systems, serving 59.5 million people, that had elevated nitrate:
- 410 systems serving 37.8 million people tested at or above 5 mg/L at least once between 2017 and 2019
- 60 systems serving almost 3.9 million people tested at or above 10 mg/L at least once
Table 1. Millions of people received drinking water with elevated nitrate (2017-2019)
|Number of systems with at least one nitrate test at or above:||Population served by the systems with at least one nitrate test at or above:|
|3 mg/L||5 mg/L||10 mg/L||3 mg/L||5 mg/L||10 mg/L|
|Large or very large systems||757||410||60||59,473,020||37,831,697||3,891,316|
EWG’s interactive map shows the locations and number of nitrate tests of each large or very large system that found nitrate in drinking water at or above 5 mg/L at least once in the three covered years. The map shows systems that tested at or above 5 mg/L because drinking water at or above this level is associated with an increased risk of adverse health effects.
Locations of drinking water systems with elevated nitrate
Elevated nitrate – 3 mg/L or above – was detected in the drinking water of large or very large systems in the vast majority of the country – 43 states. Thirty-nine states had at least one large or very large system that tested at or above 5 mg/L.
Eleven states had at least one large or very large system that tested at or above 10 mg/L, with some at much higher levels. Table 2 shows the top 10 systems with the highest nitrate tests, eight of them in California, one in Minnesota and one in Texas. All eight California systems tested at twice the legal limit or more.
Table 2. The top 10 large or very large systems with the highest nitrate tests (2017-2019)
|City or Name of Water System||State||System Size||Maximum test between 2017-2019, in mg/L|
|California Institution for Men||California||Large||43.5|
In fact, California had by far the largest number of large or very large systems with elevated nitrate from 2017 to 2019, with 168 large and 55 very large systems showing elevated nitrate, for a total of 223 systems serving 22.7 million people. Since the population of California is 39.5 million people, this means that more than half of California’s residents drank water with elevated nitrate at some point between 2017 and 2019.
Thirteen states with more than one million people were served by large or very large drinking water systems with elevated nitrate. (See Table 3.)
Table 3. States with more than 1M people served by a large or very large drinking water system with elevated nitrate
|State||Population served by large or very large systems with elevated nitrate|
California also had significantly more large or very large systems that tested nitrate at or above 5 or 10 mg/L than any other state: 168 systems serving almost 19.2 million people that tested at or above 5 mg/L, and 41 systems serving 3.4 million people that were at or above 10 mg/L.
There were only eight very large systems, serving more than 100,000 people, throughout the country that tested at or above the legal limit of 10. All were in California.
Unexpected places with elevated nitrate in drinking water
Nitrate contamination of drinking water in some Midwestern cities is well known. But EWG’s analysis reveals contamination in some surprising places, like Los Angeles and Las Vegas, among others. (See Table 4.)
Table 4. Ten very large water systems with elevated nitrate (2017-2019)
|City or Name of Water System||State||Population Served||Tests at or above 3 mg/L|
|Sacramento Suburban Water District||California||179,988||109|
|Las Vegas Valley Water District||Nevada||1,347,550||11|
Depending on the source of water for these large or very large systems, the scope of the nitrate problem shows that agriculture can pollute the drinking water of people in cities, even if the farms are far from the cities.
Groundwater systems draw their water from aquifers, which can spread across thousands of miles underground. Pollution from agriculture can contaminate the aquifer a city uses, even if the farms are many miles away from the city.
Surface water systems draw on water from lakes, reservoirs and rivers. Agricultural contaminants can run off fields upstream and end up in surface water sources downstream, away from the initial sources of farm contamination. This is the case for Des Moines, Iowa, which gets its drinking water from two rivers. Farms far upstream of the city pollute the rivers, so by the time the water reaches Des Moines, it’s full of farm chemicals.
Of the 757 large or very large systems with elevated nitrate, 52 percent used groundwater as their source of drinking water, and 48 percent used surface water.
Systems with higher levels of nitrate were slightly more likely to have groundwater as their source. Fifty-four percent of all systems at or above 5 mg/L used groundwater, and 58 percent of all systems at or above 10 mg/L used groundwater.
Solutions for the widespread nitrate problem
Keeping nitrate out of drinking water tends to be cheaper than removing it through water treatment. But prevention currently relies on farmers’ volunteering to adopt conservation practices heavily subsidized by taxpayers. The funds must go to farmers who use only the most effective practices, but even then, this strictly voluntary method is clearly not enough to keep dangerous nitrates and other farm chemicals out of drinking water.
Between 2017 and 2019, the federal government sent farmers more than $61 billion in farm subsidies to bolster their income, even though farm household income often exceeds that of nonfarm families.
It’s time for farmers to repay this generous support by adopting measures that will reduce nitrate pollution and safeguard drinking water throughout the U.S.
Mandatory farm standards that include the most effective pollution-prevention practices, in the right places and on the biggest-polluting farms, will reduce the farm chemicals that contaminate drinking water.
To conduct this analysis, EWG assessed drinking water monitoring tests for nitrate from large and very large community water systems throughout the country. According to the EPA, large systems serve between 10,001 and 100,000 people. Very large systems serve more than 100,000 people.
Some data about the water systems, such as the populations served, can be found through EPA’s SDWIS database. But EWG received the testing data by submitting public records requests to individual state agencies that regulate public drinking water, usually health or environmental departments. That data can be found in EWG’s Tap Water Database.
We analyzed the nitrate testing data for all community water systems that EPA considered active in 2021, and that conducted at least one test for nitrate between 2017 and 2019. We chose these three years because 2018 and 2019 were the years when new data was included in EWG’s 2021 Tap Water Database update. We added 2017 because some systems are only required to test for nitrate once every three years.
Water systems categorize their nitrate tests by using a contamination code of either 1040 or 1038. Some systems use both codes, but we looked only at data from each system for one code or the other, not both.
For systems that conducted more 1040 tests than 1038 between 2017 and 2019, or the same number of tests for each code, we used 1040 data. For systems with more 1038 tests than 1040 tests, we used 1038 data.
Our definition of communities with elevated nitrate includes any community water system that tested at or above 3 mg/L at least once between 2017 and 2019.
The dataset included systems that use either groundwater or surface water as their main source of drinking water. The EPA says that 3 mg/L in groundwater used for drinking water “generally indicate[s] contamination.” State health departments indicate that this level of nitrate in drinking water points to human-caused contamination, and that levels may increase over time, in both groundwater and surface water sources.
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 for people.