TEXT: Bill Stowe stands in the Nitrate Removal Facility at the Water Works treatment plant in Des Moines. Nitrate levels in the Des Moines and Raccoon rivers in 2013 were exceeding federal limits again. Stowe said it's unheard of to have spikes so high in November. Nitrate levels on the two rivers used as sources for Des Moines' drinking water often peak in the spring when rain washes unused fertilizer from farm fields.