This Wednesday, July 15, 2015 photo shows a control panel and tank in the Nitrate Removal Facility at the Des Moines Water Works plant in Des Moines, Iowa. The biggest challenge for the utility has been levels of nitrate that are far above the federal standard for safety in the two rivers that are its source water. The utility and scientists argue that the nitrates are largely the result of farm runoff that is tainted with fertilizer and manure. (AP Photo/Charlie Neibergall)