Nitrate pollution is measured differently across regions and studies: U.S. drinking-water data commonly use milligrams per liter as nitrogen, while European reporting often uses milligrams of nitrate ion per liter. The statistics below distinguish observed samples, modeled estimates, policy thresholds and future scenarios across explicit periods and geographies.
Key Nitrate Pollution Statistics
The most broadly useful figures include:
- 71% of conterminous U.S. groundwater samples contained detectable nitrate at a 0.2 mg/L threshold during 1992–1995.
- More than 15% of samples exceeded 10 mg/L as nitrogen in 4 of 33 major U.S. aquifers during 1992–1995.
- More than 5.5 million people were estimated to use drinking-water aquifers with elevated nitrate in the 2013–2021 U.S. context.
- The EPA maximum contaminant level for nitrate is 10 mg/L as nitrogen for U.S. drinking water.
- Median nitrate was 3.4 mg/L in shallow groundwater beneath U.S. agricultural land during 1992–1995.
- Median nitrate was 1.6 mg/L in shallow groundwater beneath U.S. urban land during 1992–1995.
- Median nitrate was 0.48 mg/L in deeper groundwater in U.S. major aquifers during 1992–1995.
- About 16% of U.S. agricultural-area groundwater samples exceeded the drinking-water standard through 1992.
- About 12% of domestic-supply wells in U.S. agricultural areas exceeded 10 mg/L as nitrogen in the national findings report period.
- Nitrate concentrations increased significantly in 21% of U.S. groundwater networks over the 1988–2012 comparison.
- Nitrate concentrations decreased significantly in 10% of U.S. groundwater networks over the 1988–2012 comparison.
- The share of 495 U.S. wells above 10 mg/L rose from 16% to 21% between the first and second NAWQA sampling periods.
- Average EU groundwater nitrate concentration oscillated around 21 mg NO3/L from 2000 to 2022.
- 14.1% of EU groundwater monitoring stations exceeded 50 mg NO3/L in 2016–2019.
- All 27 EU Member States reported some groundwater stations above 50 mg NO3/L in 2016–2019.
- An estimated 80% of nitrogen discharge to Europe’s aquatic environment came from agriculture in the 2024 indicator context.
- Around 30% of monitored European surface water was assessed as eutrophic under Nitrates Directive reporting.
- Around 80% of monitored European marine waters were assessed as eutrophic under the same reporting context.
- A high-ambition modeled scenario could reduce nitrogen loads to European seas by 30% by 2030.
Contents
- Key Nitrate Pollution Statistics
- U.S. Groundwater and Drinking-Water Aquifer Statistics
- Nitrate Levels by Land Use, Depth and Aquifer Condition
- U.S. Groundwater Nitrate Trends
- Private Wells and State Groundwater Exposure
- European Nitrate Pollution and Threshold Exceedances
- Sources, Eutrophication and Reduction Outcomes
U.S. Groundwater and Drinking-Water Aquifer Statistics
The USGS national assessment sampled groundwater across the conterminous United States during 1992–1995. Its 71% detection rate describes sampled groundwater, not every U.S. well or a census of all groundwater.
The assessment found nitrate more than 13 times as often as ammonia, nitrite, organic nitrogen and orthophosphate when all were evaluated at the shared 0.2 mg/L detection threshold. In four of 33 major aquifers, more than 15% of samples exceeded the 10 mg/L-as-nitrogen drinking-water level.
The U.S. regulatory benchmark is the EPA maximum contaminant level of 10 mg/L as nitrogen. This is a drinking-water threshold, not an estimate of the average concentration in groundwater.
The USGS also estimated that more than 5.5 million people used drinking-water aquifers with elevated nitrate in the 2013–2021 context. That estimate combined modeled or measured groundwater quality with population exposure and should not be read as a direct well count.
The USGS trend network provides broader monitoring context: its 25 principal aquifers represented about 75% of national groundwater withdrawals for drinking-water supply, while the nitrate trend dataset contained 1,511 wells organized into 67 networks. Coverage is therefore substantial but not equal to population-based sampling.
USGS national assessment · USGS trend assessment · EPA nitrate indicator
Nitrate Levels by Land Use, Depth and Aquifer Condition
Land use and depth produced clear differences in the 1992–1995 USGS measurements. The following medians apply to sampled groundwater and are not national means.
| Setting | Median nitrate | Period and geography |
|---|---|---|
| Shallow groundwater beneath agricultural land | 3.4 mg/L | 1992–1995, conterminous U.S. |
| Shallow groundwater beneath urban land | 1.6 mg/L | 1992–1995, conterminous U.S. |
| Deeper groundwater in major aquifers | 0.48 mg/L | 1992–1995, conterminous U.S. |
A USGS-indexed background study reported a 75th-percentile concentration of 0.51 mg/L in 81 shallow wells from relatively undeveloped areas. The same study reported 1.1 mg/L across 320 retrospective wells, with the retrospective design and relatively undeveloped classification limiting generalization.
Historical USGS findings also show how exceedances varied by supply type and land use:
- About 16% of groundwater samples from agricultural areas exceeded the drinking-water standard through 1992.
- About 1% of samples from public-supply wells exceeded the standard in that analysis through 1992.
- About 12% of domestic-supply wells in agricultural areas exceeded the 10 mg/L maximum contaminant level in the national findings report period.
Nitrate concentrations were generally highest within 100 feet of the land surface in the historical analysis. That is a directional pattern rather than a universal depth cutoff.
USGS groundwater assessment · USGS national findings
U.S. Groundwater Nitrate Trends
The USGS 1988–2012 trend assessment covered 25 principal aquifers and identified statistically significant changes in a subset of monitored networks. Twenty-one percent of networks increased, while 10% decreased; these are network-level findings, not claims about every well.
| Measure | Earlier period | Later period | Geography |
|---|---|---|---|
| Wells above 10 mg/L | 16% | 21% | 495 U.S. wells; first period 1988–1995, second 2001–2004 |
| Median agricultural shallow groundwater | 4.8 mg/L | 5.7 mg/L | U.S.; same NAWQA periods |
| Median deep groundwater in major aquifers | 1.2 mg/L | 1.5 mg/L | U.S.; same NAWQA periods |
The paired comparison shows higher later-period values for each listed measure, but it compares assessment periods rather than a continuous annual series. The two periods also have different ranges, so the figures should not be treated as a year-by-year trend line.
USGS principal-aquifer trends · USGS national findings
Private Wells and State Groundwater Exposure
Private and self-supplied systems make groundwater exposure especially relevant in some states. EPA estimates that 98% of self-supplied drinking water came from groundwater wells, while the state population shares below refer to self-supplied drinking water rather than every drinking-water system.
| State | Population using self-supplied drinking water in 2015 |
|---|---|
| Maine | 50% |
| Vermont | 39% |
| New Hampshire | 37% |
| Montana | 29% |
| Wisconsin | 28% |
EPA also modeled areas where groundwater used for drinking exceeded 10 mg/L as nitrogen. The estimates used a USGS machine-learning model at 1-km resolution, calibrated with 1988–2018 data, and rounded to whole numbers.
| State | Modeled area above 10 mg/L | Share of state area |
|---|---|---|
| Texas | 9,653 square miles | 4% |
| Kansas | 8,880 square miles | 11% |
| Oklahoma | 8,108 square miles | 12% |
| California | 2,201 square miles | 1% |
| Nebraska | 1,622 square miles | 2% |
| Colorado | 1,120 square miles | 1% |
| Pennsylvania | 772 square miles | 2% |
| New Mexico | 734 square miles | 1% |
| Iowa | 463 square miles | 1% |
These are modeled predictions for drinking-water groundwater zones, not measurements of every square mile or every private well. State population shares and modeled area shares describe different denominators and should not be compared as if they were the same exposure metric.
EPA estimated nitrate concentrations
European Nitrate Pollution and Threshold Exceedances
European Environment Agency reporting uses nitrate ion units, so its 50 mg NO3/L threshold is not interchangeable with the U.S. 10 mg/L-as-nitrogen benchmark without conversion. Average EU groundwater nitrate concentration oscillated around 21 mg NO3/L from 2000 to 2022, with no significant overall change reported.
In 2016–2019, 14.1% of EU groundwater monitoring stations exceeded 50 mg NO3/L, compared with 13.2% in 2012–2015. All 27 EU Member States reported at least some stations above 50 mg NO3/L in 2016–2019, although country-level presence does not show the share of each country’s groundwater.
Seven countries had more than 15% of stations above 50 mg NO3/L: Belgium, Cyprus, Germany, Luxembourg, Malta, Portugal and Spain. Seven others had more than 80% of stations below 25 mg/L: Croatia, Finland, Hungary, Ireland, Latvia, Poland and Sweden.
The EEA’s long series covered 475 groundwater bodies for 1992–2021, while its shorter series covered 1,025 bodies for 2000–2021. France contributed 260 bodies to the long series; Germany contributed 176 and Italy 10 to the shorter series.
These monitoring series describe reported stations or groundwater bodies rather than all European groundwater. EEA trend series use averages of annual mean concentrations and only complete time series after interpolation or extrapolation.
EEA nitrate headline indicator · EEA groundwater monitoring series
Nitrate Pollution Sources, Eutrophication and Reduction Outcomes
Nitrate pollution is part of wider nitrogen pollution, and its effects can be measured as nutrient loads or eutrophication rather than as groundwater concentration. The EEA estimated that agriculture produced 80% of nitrogen discharge to Europe’s aquatic environment in the 2024 indicator context.
Around 30% of monitored European surface water was assessed as eutrophic under Nitrates Directive reporting, while around 80% of monitored European marine waters were assessed as eutrophic. These are broader nutrient-pollution outcomes, not nitrate concentration measurements.
The EU Groundwater and Drinking Water Directives set 50 mg NO3/L as the maximum allowable nitrate concentration. The EU Green Deal target is a 50% reduction in nutrient losses by 2030, which is a policy target rather than a measured reduction.
A high-ambition modeled policy scenario projected a 30% reduction in nitrogen nutrient load to European seas by 2030 and a 20% reduction in phosphorus load. Those are forecasts, and the phosphorus figure is not a nitrate result.
EEA nitrate headline indicator