A new study of private wells shows nitrate levels have increased over the past 15 years, and only a fraction of wells are being tested.

The Iowa Environmental Council and the Environmental Working Group analyzed test results from 2002 to 2017. In that time, average nitrate levels rose from 3.1 milligrams per liter in 2003 to 5.7 milligrams per liter in 2013. The drinking water standard is 10 milligrams per liter, but limited studies have shown illnesses caused by lower concentrations.

More than 6,600 wells, or 12 percent of those tested, had nitrate averages at or above the EPA’s health standard for drinking water.

Nitrate, which occurs naturally and is linked to farm fertilizers, has been associated with a condition that suffocates babies, and with cancers and miscarriages. 

The study found that 55,000 of an estimated 230,000 to 290,000 private Iowa wells were tested for nitrate or fecal bacteria, which was found in more than 40 percent of wells tested. 

“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.”