Groundwater is a major source of freshwater, irrigation supply and drinking water, but its scale and condition vary sharply by region. The statistics below distinguish withdrawals, storage trends, modeled quality, exposure-risk estimates and sampled well results by period and geography.
Key Groundwater Statistics
The following figures summarize the most useful measures across the global and U.S. evidence:
- In 2017, 959 km³ of groundwater per year was withdrawn worldwide, according to an estimate covering global freshwater use.
- In 2017, groundwater represented 25% of total freshwater withdrawals worldwide.
- In 2017, Asia withdrew 657 km³ of groundwater per year, including South Asia’s 401 km³.
- In 2017, Western Asia obtained 39% of its total freshwater withdrawals from groundwater.
- In 2017, North America withdrew 156 km³ of groundwater per year.
- In 2017, Northern Africa withdrew 26.2 km³ of groundwater per year, 24% above its 2010 estimate.
- In 2015, U.S. groundwater withdrawals totaled about 84,600 million gallons per day.
- In 2015, fresh groundwater supplied 97% of U.S. groundwater withdrawals, or 82,300 million gallons per day.
- In 2015, California accounted for 21% of U.S. groundwater withdrawals.
- From 1900 through 2008, U.S. groundwater depletion totaled approximately 1,000 km³.
- During 2000–2008, average U.S. groundwater depletion reached almost 25 km³ per year.
- From 2002–2022, 53% of mapped groundwater-dependent ecosystem area with trend data lay in declining-storage regions.
- In a global synthesis, 34% of groundwater samples exceeded the WHO nitrate threshold of 50 mg/L as nitrate.
- In the same synthesis, median groundwater nitrate was 5.5 mg/L across 2,291 samples, compared with 0.3 mg/L in rivers.
- A 2024 review estimated 300–500 million people at risk of severe health impacts from geogenic groundwater contaminants.
- A global review estimated more than 230 million people at risk from arsenic-contaminated groundwater, including 180 million in Asia.
- In the United States, more than 43 million people relied on private wells for drinking water.
- In a USGS study of 2,100 U.S. private wells, about one in five wells had at least one contaminant above a human-health benchmark.
Contents
- Global groundwater withdrawals and regional water use
- U.S. groundwater use, aquifers and irrigation
- Groundwater depletion and storage trends
- Groundwater quality and nitrate statistics
- Arsenic and geogenic contamination risks
- Groundwater access, private wells and ecosystems
Global Groundwater Withdrawals and Regional Water Use
The United Nations World Water Development Report estimated global groundwater withdrawal at 959 km³ per year in 2017, equal to 25% of total freshwater withdrawals worldwide. These are compiled estimates from Aquastat, Eurostat and published estimates, not direct measurements of groundwater storage or recharge. The United Nations World Water Development Report 2022: Groundwater: Making the invisible visible
Regional withdrawal estimates show how uneven use is:
| Region | 2017 groundwater withdrawal | Measurement context |
|---|---|---|
| Asia | 657 km³/year | Regional estimate |
| South Asia | 401 km³/year | Regional estimate |
| East Asia | 132 km³/year | Regional estimate |
| Southeast Asia | 54.2 km³/year | Regional estimate |
| North America | 156 km³/year | Regional estimate |
| Africa | 45 km³/year | Regional estimate |
| Southern Europe | 29.7 km³/year | Regional estimate |
| Australia and Oceania | 8 km³/year | 21% above 2010 estimate |
The same 2017 table reported that Western Asia obtained 39% of total freshwater withdrawals from groundwater, while Central America obtained 38%. Northern Africa withdrew 26.2 km³ per year, 24% above its 2010 estimate, whereas Europe withdrew 65 km³ per year, 6% below its 2010 estimate.
The regional table uses 2017 withdrawals and reports percentage change from 2010; definitions and source coverage vary by region. A withdrawal total should not be interpreted as a measure of recharge, sustainable yield or the population served.
U.S. Groundwater Statistics: Use, Aquifers and Irrigation
U.S. Geological Survey estimates provide a separate national view. In 2015, total U.S. groundwater withdrawals were about 84,600 million gallons per day, and principal aquifers supplied about 94%, or 79,200 million gallons per day.
Principal aquifers are regionally extensive aquifers with suitable potential quantity and quality. Estimated Groundwater Withdrawals from Principal Aquifers in the United States, 2015
Freshness and state concentration add important definitions:
- Fresh groundwater accounted for 97% of U.S. groundwater withdrawals in 2015, or 82,300 million gallons per day.
- California accounted for 21% of national groundwater withdrawals in 2015.
- Arkansas accounted for 11%, Texas 9%, Nebraska 7% and Idaho 6% of U.S. groundwater withdrawals in 2015.
These state percentages were calculated from unrounded USGS values, while the national totals are rounded estimates. Groundwater Use
Irrigation is a particularly large use category. In water year 2020, groundwater extraction for irrigation was about 65,406 million gallons per day and represented 65% of all irrigation applications in the conterminous United States.
Globally, a contemporary estimate cited in a Nature commentary attributes about 70% of groundwater use to irrigation; that denominator is groundwater use, not all irrigation water. Rapid groundwater decline and some cases of recovery in aquifers globally
Groundwater Depletion Statistics and Storage Trends
A USGS assessment estimated approximately 1,000 km³ of U.S. groundwater depletion from 1900 through 2008. Average depletion was 9.2 km³ per year over the full period, rising to almost 25 km³ per year during 2000–2008; the reported later-period rate was about 2.7 times the full-period average. Groundwater depletion in the United States (1900−2008)
A global study measured groundwater-level trends using about 170,000 wells and 1,693 aquifer systems in more than 40 countries. Its coverage represented approximately 75% of global groundwater withdrawals, but historical comparison was possible for only about one-third of mapped aquifers and coverage was uneven. Rapid groundwater decline and some cases of recovery in aquifers globally
Groundwater-dependent ecosystem data show why storage trends matter beyond wells:
| Area or region | Declining-storage share, 2002–2022 | Scope |
|---|---|---|
| Mapped GDE area overall | 53%, or 3.81 million km² | 7.20 of 8.34 million km² with trend data |
| Europe dryland GDEs | 90% | Mapped area |
| Asia dryland GDEs | 75% | Mapped area |
| North America dryland GDEs | 65% | Mapped area |
The ecosystem analysis used GRACE-derived trends, which are coarse and vertically integrate shallow and deep groundwater. Local ecosystem effects can therefore differ substantially from the mapped regional pattern. Groundwater-dependent ecosystem map exposes global dryland protection needs
Groundwater Quality Statistics: Nitrate in Wells and Aquifers
EPA’s nitrate indicator uses a 10 mg/L maximum contaminant level for nitrate in groundwater used for drinking. Interpretive thresholds are different: concentrations above 3 mg/L generally indicate contamination, while concentrations above 1 mg/L indicate human activity in a cited nationwide study; neither threshold is a universal health limit. Estimated Nitrate Concentrations in Groundwater Used for Drinking
The USGS model behind the EPA indicator used measured nitrate data from 12,082 wells, with calibration data collected from 1988–2018 in the conterminous United States. It predicted, at 1-km resolution, 2,201 square miles in California above 10 mg/L, 8,880 square miles in Kansas, or 11% of state area, and 189 square miles in Delaware, or 10% of state area.
Those state figures are modeled areas in drinking-water zones, not direct well-by-well prevalence or percentages of residents exposed. The map is therefore useful for geographic screening, while individual well testing remains a separate measurement question.
A global synthesis of adjacent shallow aquifers found median groundwater nitrate of 5.5 ± 5.1 mg/L across 2,291 samples. About 34% of groundwater samples exceeded the WHO threshold of 50 mg/L as nitrate, compared with about 2% of 2,902 river samples; median river nitrate was 0.3 ± 0.2 mg/L.
The synthesis also reported mean groundwater nitrate δ15N of +7.7 ± 4.5‰ across 2,291 aquifer samples and δ18O of +2.3 ± 5.4‰ across 2,235 measurements. These isotope values indicate source or process information rather than nitrate concentration, and the compiled dataset is geographically uneven. Global patterns of nitrate isotope composition in rivers and adjacent aquifers reveal reactive nitrogen cascading
Arsenic and Geogenic Groundwater Contamination Risks
A 2024 review estimated that 300–500 million people are at risk of severe health impacts and premature mortality from geogenic groundwater contaminants, including arsenic, fluoride, selenium and uranium. The review also reported that up to 60% of groundwater sources are contaminated above recommended concentrations in some regions; this is an upper regional bound, not a global average. Arsenic and other geogenic contaminants in global groundwater
Arsenic-specific estimates are also broad:
- A global review found arsenic contamination beyond recommended concentrations across nearly 108 countries.
- More than 230 million people were estimated to be at risk from arsenic-contaminated groundwater, including 180 million in Asia.
- The review identified affected countries in Asia (32), Europe (31), Africa (20), North America (11), South America (9) and Australia (4).
These are literature-review estimates with uneven monitoring, and the affected-country counts do not measure affected-area shares. The risk figures are not confirmed disease counts or a current census of exposed residents.
A separate global model estimated 605–1,814 teragrams of nitrate stored in the vadose zone at peak during 1900–2000. That is a model-based storage estimate rather than a direct global measurement, and it describes nitrate storage above the saturated zone rather than a count of contaminated wells. Global patterns of nitrate storage in the vadose zone
Groundwater Access, Private Wells and Ecosystem Dependence
In the United States, EPA estimates that about 15% of the population, or more than 43 million people, relied on private wells for drinking water, and more than 23 million households used private wells. These figures concern private domestic wells and are rounded estimates. Private Drinking Water Wells
Private-well quality results show why access statistics do not automatically describe safety:
- About one in five wells in a USGS study of 2,100 private wells had at least one contaminant above a human-health benchmark.
- EPA reports that 98% of self-supplied U.S. drinking-water systems draw from groundwater wells; this applies to self-supplied drinking water, not all U.S. drinking water.
- In 2015, groundwater supplied 51% of public-supply withdrawals in the conterminous United States.
The private-well study sample is not necessarily nationally representative, and a benchmark exceedance is not a diagnosis. Likewise, a withdrawal share is not a population share: the 51% public-supply figure describes water withdrawn, while the 15% private-well figure describes people.
Together, these measures show why groundwater statistics need a defined denominator. A global withdrawal estimate, a modeled contaminant area, a sampled-well exceedance rate and a population relying on wells describe different parts of the groundwater system and should not be combined into one exposure or sustainability score.