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Pollution of surface and groundwater by inorganic nitrogen (N) was assessed in farm villages of northern Vietnam. The pH and ammonium-N and nitrate-N concentrations were monitored at three communes near Ha Noi in the Red River Delta in March and September 2003, following monitoring in October 2002. In each monitoring time, ammonium-N concentrations exceeded the Vietnamese water standards applicable to surface and groundwater, whereas the nitrate-N concentrations were relatively low and below the corresponding standards. Neither spatial nor temporal variation was found in the ammonium-N and nitrate-N concentrations of the surface water. A temporal increase in the ammonium-N concentration was statistically confirmed in the groundwater. Intensively applied fertilizer-N and disposed animal/human wastes were thought to be sources of ammonium-N. Ammonium-N originating from those sources was seen to accumulate steadily in the groundwater through percolation from the surface water and surrounding land. A spatial variation of the nitrate-N concentration was observed in the groundwater. The nitrate-N concentration in the groundwater was particularly low in communes located in lowland areas with

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