From 2,200 feet in the air, Boone County looks like a green quilt. Square fields of corn and soybeans are stitched together by county roads. On the horizon, the pattern is interrupted by a wide, blue ribbon. It curves back and forth over the landscape, surrounded by a dark mass of trees on either side.
This is the Des Moines River. Stretching from southwest Minnesota to southeast Iowa, it drains some of the most productive farmland in the U.S. into the Mississippi River.
It’s also one of the main drinking water sources for around 600,000 people in the Des Moines area. Elevated nitrate levels in the Des Moines and Raccoon rivers this spring and summer pushed Central Iowa Water Works (CIWW), the regional drinking water utility, to issue its first lawn watering ban from June 12 to July 21.
The restriction dropped demand by more than 30%, allowing CIWW to pump water through extra treatment steps and stay under the federal safe drinking water limit for nitrate…