2012 saw a drought in the American mid-west.  As a result, withered corn plants didn't suck up all the nitrogen spread on fields.  

But 2013 gave Iowa citizens the wettest April in 141 years, and that rain washed the unused fertilizer into rivers, the primary source of drinking water for 45 percent of the state's population. 

The problem will pass, but nitrate levels will always be a worry which has reached levels never seen in Iowa. Nitrogen is crucial because corn requires so much of it but Iowa is especially vulnerable to nitrate level concerns because about 90 percent of the state is dedicated to agriculture.

"These numbers are so high that they're not only problematic from an ecological standpoint for the rivers, lakes, ponds, and reservoirs, but they become a real issue for human health," said Bob Hirsch, a research hydrologist for the U.S. Geological Survey who studies long-term changes in river water quality.

If only science could come up with a technology that required less fertilizer in agriculture.

Iowa copes with nitrate surge in drinking water by David Pitt, Associated Press