Dissolved organic nitrogen (DON) is an issue for the water field primarily due to the formation of disinfection by-products of health concern, and its potential role in membrane fouling. This article reviews the following DON issues: (1) analytical measurement, (2) occurrence, (3) structural composition, and (4) treatability during potable water treatment. There is no direct measurement for DON, rather DON is calculated by the difference between total dissolved nitrogen and inorganic nitrogen ions. DON concentrations range from <0.1 to >10 mg N/l with a median value of ∼0.3 mg N/l in surface waters. DON sources include wastewater discharges, agricultural fertilizers, algae, forest litter and soils. DON is comprised of a broad spectrum of molecular weight compounds encompassing multiple N-containing functional groups. Carbon to nitrogen ratios (C/N or DOC/DON) range between 5 and 100 mg C/mg N (median ∼15 mg C/mg N), and may be a good indicator of organic matter sources. During chlorination higher org-N content leads to (1) increasing chlorine demand, (2) production of di-HAA>tri-HAA, (3) production of HAA>THM, and (4) production of higher levels for halogenated (nitromethanes, HANs) and non-halogenated (NDMA) org-N DBPs. Information on DON removal during potable water treatment is lacking and should be a focus of future research.

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