Natural nitrate levels in groundwater are generally very low (typically less than 10 mg/l NO3), but nitrate concentrations grow due to human activities, such as agriculture, industry, domestic effluents and emissions from combustion engines. The following table  shows the causes of nitrates pollution in groundwater.
Nitrates generally moves relatively slow in soil and groundwater: there is a lag time of approximately 20 years between the pollution activity and the detection of the pollutant in groundwater. For this reason, it is predicted that current polluting activities will continue to affect nitrate concentrations for several decades. However if the pressure in the aquifer is high, transport can be very rapid within the saturation zone.
The sources of nitrates pollution in groundwater are:
cultivation in areas where the soil layer is relatively thin, or has poor nutrient buffering capacity, or where there are changes in land use;
over fertilization of crop for intensification of agricultural activity;
spread cultivation of crops which require high fertilizes doses and which leave the soil bare over long periods (maize, tobacco and vegetables);
drainage systems which lead to drainage of fertilizers;
intensive agricultural rotation cycles involving frequent ploughing and extensive areas of bare soils during winters;
organic fertilizers form animal husbandry;
For more information and for the heath effects of nitrate in drinking water click on our nitrate web page.
Click here for general information about groundwater contaminants. Check also seawater intrusions, arsenic and iron in groundwater.
For more information check the following pages: groundwater contamination, quality, source of groundwater pollution, reducing groundwater contamination.
Click here for definitions concerning groundwater, or to learn more about its properties, its origin and quantities, its sources in Europe.