Public Supply Wells
What’s in the Groundwater Used for Public Supply?
USGS studies the quality of this key source of drinking water
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Are you among the more than 100 million people in the U.S. who relies on a public-supply well for your drinking water? Although the quality of finished drinking water from public water systems is regulated by the EPA, long-term protection and management of the raw groundwater tapped by public-supply wells requires an understanding of the occurrence of contaminants in this invisible, vital resource.
The USGS National Water Quality Program investigates the quality of water pumped from public-supply wells across the United States. These wells are the source of drinking water and water for other household needs for more than one-third of the U.S. population. There are about 140,000 public water systems that use groundwater as their source.
Population relying on public wells for drinking water (image is from USGS Circular 1346).
Although the quality of finished drinking water (after treatment and before distribution) from these public water systems is regulated by the EPA under the Safe Drinking Water Act (SDWA), long-term protection and management of groundwater, a vital source of drinking water, requires an understanding of the occurrence of contaminants in untreated source water. Sources of drinking water are potentially vulnerable to a wide range of manmade and naturally occurring contaminants, including many that are not regulated in drinking water under the SDWA.
Water Quality of Public Supply Wells
In a study of 932 U.S. public-supply wells, water pumped from about one in five source-water samples (that is, before treatment) contained one or more contaminants at a concentration greater than a human-health benchmark for drinking water. Supporting information and summary data for the study can be found here.
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Naturally occurring trace elements and radionuclides accounted for about three-quarters of contaminant concentrations greater than human-health benchmarks in source-water samples.
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Manmade organic compounds, such as pesticides and solvents, were detected in nearly two-thirds of samples, but typically at a concentration that did not exceed a human-health benchmark.
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Many organic (manmade) contaminants detected in source water also were detected in treated water at similar concentrations.
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Human-health benchmarks are not yet available for many manmade contaminants, including some that were frequently detected in source water.
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Contaminants found in groundwater used as a source of public supply usually co-occurred with other contaminants as mixtures, rather than alone, which is a potential concern because the total toxicity of a mixture can be greater than that of any single contaminant.
Public wells where water samples were collected and sampled for chemical contaminants (image is from USGS Circular 1346).
Read informative fact sheets about current water-quality conditions in public supply wells that pump water from Principal Aquifers across the country. More detailed information on the quality of water from public-supply wells is provided in USGS publications that summarize the quality of water in Principal Aquifers in nine regions of the United States.
What causes public-supply wells to be vulnerable to contamination?
Public-supply-well vulnerability to contamination starts with groundwater vulnerability to contamination. The vulnerability of the water from public-supply wells to contamination depends on contaminant input in the area that contributes water to a well, the mobility and persistence of a contaminant once released to the groundwater, and the ease of groundwater and contaminant movement from the point of recharge to the well. Wells within a single aquifer, however, may not be equally vulnerable to contaminants in the aquifer because individual wells produce unique mixtures of the groundwater from different depths in the aquifer and with different ages (time since recharge).
A study done from 2001 to 2011 sheds light on factors that affect the vulnerability of water from public-supply wells to contamination. The study also identified measures that can be used to determine which factor (or factors) plays a dominant role at an individual public-supply well. These measures are particularly useful for indicating which contaminants in an aquifer might reach an individual public-supply well and when, how, and at what concentration they might arrive. Case-study examples show how such information can be used to improve water quality.
Interested in the water quality of domestic (private) wells?
Find information on USGS studies of domestic water-supply wells used for drinking water by thousands of people in rural areas.
Explore these topics related to groundwater quality:
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Date published: March 2, 2019Status: ActiveGroundwater Quality Research
Every day, millions of gallons of groundwater are pumped to supply drinking water for about 140 million people, almost one-half of the Nation’s population. Learn about the quality and availability of groundwater for drinking, where and why groundwater quality is degraded, and where groundwater quality is changing.
Attribution: Water Resources, National Water Quality Program -
Date published: February 28, 2019Status: ActivePredicting Groundwater Quality in Unmonitored Areas
Groundwater provides nearly one-half of the Nation’s drinking water, and sustains the steady flow of streams and rivers and the ecological systems that depend on that flow. Unless we drill a well, how can we know the quality of the groundwater below? Learn about how the USGS is using sophisticated techniques to predict groundwater quality and view national maps of groundwater quality.
Contacts: Paul StackelbergAttribution: Water Resources, National Water Quality Program -
Date published: February 28, 2019Status: ActiveRapid Fluctuations in Groundwater Quality
We think of groundwater as moving slowly, and groundwater quality as changing slowly—over decades or even centuries. But in some parts of some aquifers, groundwater quality can fluctuate rapidly, sometimes over just a few hours. Are such changes part of a long-term trend, or just part of a short-term cycle? And what does that mean for suitability for drinking?
Contacts: Justin KulongoskiAttribution: Water Resources, National Water Quality Program -
Date published: March 2, 2019Status: ActiveGroundwater/Surface-Water Interaction
Water and the chemicals it contains are constantly being exchanged between the land surface and the subsurface. Surface water seeps into the ground and recharges the underlying aquifer—groundwater discharges to the surface and supplies the stream with baseflow. USGS Integrated Watershed Studies assess these exchanges and their effect on surface-water and groundwater quality and quantity.
Contacts: Paul D CapelAttribution: Water Resources, National Water Quality Program -
Date published: February 28, 2019Status: CompletedFactors Affecting Vulnerability of Public-Supply Wells to Contamination
More than 100 million people in the United States—about 35 percent of the population—receive their drinking water from public-supply wells. These systems can be vulnerable to contamination from naturally occurring constituents, such as radon, uranium and arsenic, and from commonly used manmade chemicals, such as fertilizers, pesticides, solvents, and gasoline hydrocarbons. Learn about the...
Contacts: Sandra EbertsAttribution: Water Resources, National Water Quality Program
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Year Published: 2010Quality of Water from Public-Supply Wells in the United States, 1993-2007Overview of Major Findings
Summary of Major Findings and Implications About 105 million people in the United States-more than one-third of the Nation's population-receive their drinking water from about 140,000 public water systems that use groundwater as their source. Although the quality of finished drinking water (after treatment and before distribution) from these...
Toccalino, Patricia L.; Hopple, Jessica A.Attribution: Water ResourcesView CitationQuality of Water from Public-Supply Wells in the United States, 1993-2007Overview of Major Findings; 2010; CIR; 1346; Toccalino, Patricia L.; Hopple, Jessica A.
Assessing the lead solubility potential of untreated groundwater of the United States
In the U.S., about 44 million people rely on self-supplied groundwater for drinking water. Because most self-supplied homeowners do not treat their water to control corrosion, drinking water can be susceptible to lead (Pb) contamination from metal plumbing. To assess the types and locations of susceptible groundwater, a geochemical reaction model...
Jurgens, Bryant; Parkhurst, David L.; Belitz, Kenneth Hormones and pharmaceuticals in groundwater used as a source of drinking water across the United States
This is the first large-scale, systematic assessment of hormone and pharmaceutical occurrence in groundwater used for drinking across the United States. Samples from 1091 sites in Principal Aquifers representing 60% of the volume pumped for drinking-water supply had final data for 21 hormones and 103 pharmaceuticals. At least one compound was...
Bexfield, Laura M.; Toccalino, Patricia; Belitz, Kenneth; Foreman, William T.; Furlong, Edward Radium mobility and the age of groundwater in public-drinking-water supplies from the Cambrian-Ordovician aquifer system, north-central USA
High radium (Ra) concentrations in potable portions of the Cambrian-Ordovician (C-O) aquifer system were investigated using water-quality data and environmental tracers (3H, 3Hetrit, SF6, 14C and 4Herad) of groundwater age from 80 public-supply wells (PSWs). Groundwater ages were estimated by calibration of tracers to lumped...
Stackelberg, Paul E.; Szabo, Zoltan; Jurgens, Bryant C. Domestic well locations and populations served in the contiguous U.S.: 1990
We estimate the location and population served by domestic wells in the contiguous United States in two ways: (1) the “Block Group Method” or BGM, uses data from the 1990 census, and (2) the “Road-Enhanced Method” or REM, refines the locations by using a buffer expansion and shrinkage technique along roadways to define areas where domestic wells...
Johnson, Tyler; Belitz, Kenneth
The quality of our Nation's waters: Water quality in basin-fill aquifers of the southwestern United States: Arizona, California, Colorado, Nevada, New Mexico, and Utah, 1993-2009
The Southwest Principal Aquifers consist of many basin-fill aquifers in California, Nevada, Utah, Arizona, New Mexico, and Colorado. Demands for irrigation and drinking water have substantially increased groundwater withdrawals and irrigation return flow to some of these aquifers. These changes have increased the movement of contaminants from...
Thiros, Susan A.; Paul, Angela P.; Bexfield, Laura M.; Anning, David W.
The quality of our Nation's waters: groundwater quality in the Columbia Plateau and Snake River Plain basin-fill and basaltic-rock aquifers and the Hawaiian volcanic-rock aquifers, Washington, Idaho, and Hawaii, 1993-2005
The Columbia Plateau, Snake River Plain, and Hawaii are large volcanic areas in the western United States and mid-Pacific ocean that contain extensive regional aquifers of a hard, gray, volcanic rock called basalt. Residents of the Columbia Plateau, the Snake River Plain, and the island of Oahu depend on groundwater as their primary source of...
Rupert, Michael G.; Hunt, Charles D.; Skinner, Kenneth D.; Frans, Lonna M.; Mahler, Barbara J.
The quality of our Nation's waters: water quality in the Denver Basin aquifer system, Colorado, 2003-05
Availability and sustainability of groundwater in the Denver Basin aquifer system depend on water quantity and water quality. The Denver Basin aquifer system underlies about 7,000 square miles of the Great Plains in eastern Colorado and is the primary or sole source of water for domestic and public supply in many areas of the basin. Use of...
Bauch, Nancy J.; Musgrove, MaryLynn; Mahler, Barbara J.; Paschke, Suzanne
The quality of our Nation's waters: water quality in the Northern Atlantic Coastal Plain surficial aquifer system, Delaware, Maryland, New Jersey, New York, North Carolina, and Virginia, 1988-2009
The surficial aquifer system of the Northern Atlantic Coastal Plain is made up of unconfined aquifers that underlie most of the area. This aquifer system is a critical renewable source of drinking water and is the source of most flow to streams and of recharge to underlying confined aquifers. Millions of people rely on the surficial aquifer system...
Denver, Judith M.; Ator, Scott W.; Fischer, Jeffrey M.; Harned, Douglas C.; Schubert, Christopher E.; Szabo, Zoltan
The quality of our Nation's waters: water quality in the Upper Floridan aquifer and overlying surficial aquifers, southeastern United States, 1993-2010
About 10 million people rely on groundwater from the Upper Floridan and surficial aquifers for drinking water. The Upper Floridan aquifer also is of primary importance to the region as a source of water for irrigation and as a source of crystal clear water that discharges to springs and streams providing recreational and tourist destinations and...
Berndt, Marian P.; Katz, Brian G.; Kingsbury, James A.; Crandall, Christy A.
The quality of our Nation's waters: water quality in the glacial aquifer system, northern United States, 1993-2009
The glacial aquifer system underlies much of the northern United States. About one-sixth (41 million people) of the United States population relies on the glacial aquifer system for drinking water. The primary importance of the glacial aquifer system is as a source of water for public supply to the population centers in the region, but the aquifer...
Warner, Kelly L.; Ayotte, Joseph D.
The quality of our nation's waters: water quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions, eastern United States, 1993-2009
The aquifers of the Piedmont, Blue Ridge, and Valley and Ridge regions underlie an area with a population of more than 40 million people in 10 states. The suburban and rural population is large, growing rapidly, and increasingly dependent on groundwater as a source of supply, with more than 550 million gallons per day withdrawn from domestic wells...
Lindsey, Bruce D.; Zimmerman, Tammy M.; Chapman, Melinda J.; Cravotta, Charles A.; Szabo, Zoltan Modeling nitrate at domestic and public-supply well depths in the Central Valley, California
Aquifer vulnerability models were developed to map groundwater nitrate concentration at domestic and public-supply well depths in the Central Valley, California. We compared three modeling methods for ability to predict nitrate concentration >4 mg/L: logistic regression (LR), random forest classification (RFC), and random forest regression (RFR...
Nolan, Bernard T.; Gronberg, JoAnn M.; Faunt, Claudia C.; Eberts, Sandra M.; Belitz, Ken-
Date published: March 4, 2019Groundwater Quality: Decadal Change
Almost one-half of the U.S. population rely on groundwater for their water supply, and demand for groundwater for public supply, irrigation, and agriculture continues to increase. This mapper shows how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.
Attribution: Water Resources, Upper Midwest Water Science Center
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Date published: March 4, 2019
Groundwater Quality: Decadal Change
Almost one-half of the U.S. population rely on groundwater for their water supply, and demand for groundwater for public supply, irrigation, and agriculture continues to increase. This mapper shows how concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater are changing during decadal periods across the Nation.
Attribution: Water Resources -
Date published: March 4, 2019Predicted pH at the domestic and public supply drinking water depths, Central Valley, California
This scientific investigations map is a product of the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) project modeling and mapping team. The prediction grids depicted in this map are of continuous pH and are intended to provide an understanding of groundwater-quality conditions at the domestic and public supply drinking water zones in the groundwater of the Central Valley.
Attribution: Water Resources -
Date published: March 4, 2019Volatile Organic Compounds in Samples from Domestic and Public Wells, 1985–2002
The U.S. Geological Survey’s (USGS) National Water-Quality Assessment (NAWQA) Program recently completed a national study of volatile organic compounds (VOCs) in the Nation’s ground water (Zogorski and others, 2006). Part of this assessment emphasizes the occurrence of 55 VOCs in samples from 2,401 domestic wells and 1,096 public wells during 1985–2002.
Attribution: Water Resources