Dissolved organic nitrogen (DON) was measured in drinking waters and wastewaters during multiple sampling campaigns. DON analysis used a new dialysis based pretreatment method. On average, DON measured in 28 drinking water treatment plant influents was determined to be 0.16 mg-N/L. In wastewater effluents, DON concentrations varied between 0.51-1.1 mg-N/L. Additionally, organic nitrogen in dissolved organic matter isolates was characterized. A significant fraction (20 - 65 %) of the dissolved organic matter present in samples rich in organic nitrogen samples was of colloidal nature having an average carbon to nitrogen ratio of 7.7.