Iowa's Private Wells Overrun With Agricultural Contaminants

posted on Wednesday, April 24, 2019 in Water and Land News

Des Moines, IA -- Private wells across Iowa are contaminated with unsafe levels of two agricultural contaminants, according to an investigation by the Environmental Working Group and the Iowa Environmental Council.

The groups’ analysis of state records from 2002 to 2017 found that thousands of private wells tested positive for coliform bacteria as well as nitrate, a chemical found in fertilizer and animal manure that is linked to cancer and birth defects. Both bacteria – including fecal coliforms like E. coli – and nitrate commonly enter waterways and groundwater in runoff from farms, and both contaminants are linked to severe human health problems.

“The state’s own data show that agricultural pollution of drinking water in Iowa is worse than most people have previously thought,” said Anne Schechinger, senior economic analyst at EWG and the study’s primary author. “Wherever Iowans test for these contaminants, they have a pretty good chance of finding them.”

An estimated 230,000 to 290,000 Iowans rely on private wells for their household drinking water. Yet over the 16 years examined in the study, only 55,000 wells in the state were tested for nitrate, bacteria, or both.

Of those, more than 22,000 wells – more than 40 percent – tested positive for coliform bacteria at least once. Over 4,300 wells were positive for bacteria every time they were tested, showing ongoing contamination problems. The Environmental Protection Agency says there is no safe level of coliform bacteria in drinking water, because the bacteria indicate the presence of other harmful pathogens.

More than 6,600 wells, or 12 percent of those tested, had nitrate averages at or above the EPA’s legal limit for drinking water systems. That standard is 10 parts per million, or ppm, and is based on science from the 1950s. (A part per million is equivalent to one milligram per liter, or mg/L.) More than 12,300 Iowa wells – 22 percent – had nitrate levels at or above 5 ppm, the threshold at which many more recent studies have found an increased risk of colon, bladder, ovarian, kidney and rectal cancer, as well as birth defects.

Private Well Contamination

EWG’s and IEC’s analysis showed a steady growth in nitrate levels across the state: The average level of nitrate contamination in private wells nearly doubled between 2002 and 2017, from 3.1 ppm in 2003 to 5.7 ppm in 2013.

“There’s a clear pattern of widespread private well contamination across Iowa that is growing worse for nitrate and staying steadily bad for bacteria,” said Cindy Lane, water program director for the Iowa Environmental Council. “But we don’t even have information on the thousands of wells that were not tested during this period. That makes me worry that the problem is even more serious than documented.”

The Iowa Department of Natural Resources recommends that well owners test wells at least once a year but does not require it. Only 10 wells in the entire state were tested every year for nitrate, and only 12 wells were tested every year for bacteria. Almost two-thirds of all wells were tested only once between 2002 and 2017, even if that test showed unsafe levels of bacteria or nitrate.

The state requires newly dug or renovated wells to be tested for nitrate and coliform bacteria but does not require follow-up tests. Testing of already established wells is at the owners’ discretion. The state does provide funds for residents to test their wells voluntarily, but implementation varies widely among counties.

Some of the counties whose tests showed the highest concentration of nitrate and highest percentages of wells with bacteria present had the fewest tests of all, which shows that residents of areas with the biggest problems may be getting the least support.

The EPA, which sets and enforces federal drinking water standards for water utilities, does not regulate private well testing or treatment for the estimated 43 million Americans who rely on private wells for their drinking water.

“This study has shined a light on a huge loophole in federal drinking water standards,” Schechinger said. “And not everyone can dig their way out of it with a new well.”


  1. drinking water
  2. nitrate pollution
  3. public health
  4. water quality