More than 43 million people—about 15 percent of the U.S. population—rely on domestic (private) wells as their source of drinking water. The quality and safety of water from domestic wells are not regulated by the Federal Safe Drinking Water Act or, in most cases, by state laws. Instead, individual homeowners are responsible for maintaining their domestic well systems and for monitoring water quality.
Featured: 3-D Models of As and Mn in the Glacial Aquifer System
New 3-D models from the USGS National Water Quality Program predict where high concentrations of arsenic and manganese likely occur in the glacial aquifer system, groundwater supply for 30 million. Redox conditions and pH are controlling factors.
Featured Study: Lithium in the Nation's Groundwater
Got lithium? A new USGS study reports that about 45% of public-supply wells and about 37% of U.S. domestic supply wells have concentrations of lithium that could present a potential human-health risk.
The USGS National Water Quality Program investigates the quality of water pumped from domestic wells across the United States. These wells are the sole source of drinking water and water for other household needs for most people in many rural areas. Health risks associated with contaminants in domestic well water include gastrointestinal illness related to bacteria and other pathogens and exposure to elevated concentrations of nitrate, arsenic, radon, lead, and organic compounds. Typically, the water supplied by domestic wells is not routinely tested. As a result, people using domestic-supply wells could be drinking water with elevated concentrations of some contaminants.
The quality and safety of water from privately owned domestic wells is not regulated under Federal or, in most cases, state laws. Homeowners are primarily responsible for maintaining their domestic well systems and for any water-quality monitoring. Federal regulations under the Safe Drinking Water Act (SDWA) for public water supplies, although not directly applicable to the regulation of domestic wells, provide useful concentration benchmarks for evaluating the quality of water from domestic wells in a human-health context.
Water Quality of Domestic Wells
In a study of 2,100 domestic wells, water pumped from about one in five wells 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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The contaminants most often found at these elevated concentrations were inorganic chemicals, such as metals, radionuclides, and nitrate; all of these but nitrate are derived primarily from natural sources.
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Man-made organic compounds, such as pesticides and solvents, were detected in more than half (60 percent) of the domestic wells sampled, but concentrations were seldom greater than human-health benchmarks (less than 1 percent of wells).
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About half of the wells had at least one “nuisance” contaminant—a compound that impairs taste, odor, or other aesthetic considerations—at a level or concentration outside the range of values recommended by the U.S. Environmental Protection Agency.
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Microbial contaminants (for example, bacteria) were detected in about one-third of the approximately 400 wells that had their water analyzed for those contaminants.
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Contaminants found in domestic wells 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.
More information on the quality of water from domestic wells is provided in USGS publications that summarize the quality of water in Principal Aquifers in nine regions of the United States and specifically groundwater tapped by domestic wells in Principal Aquifers.
Where Are Domestic Wells Used?
USGS maps show where people across the Nation rely on private wells for their drinking water. The maps estimate the number of people using private wells in a given area, but individual wells are not identified. The maps can help determine where focused groundwater-quality testing or further studies are needed to help ensure safe drinking water from private wells. For instance, overlaying information on private well use with a map of potentially corrosive groundwater could be used to focus water-quality testing for lead in areas with a high density of private wells and a high likelihood of potentially corrosive groundwater.
Types of Domestic Wells
There are several types of domestic wells used by homeowners. The oldest wells were dug by hand. These wells typically are shallow and of large diameter (several feet), and may be lined with stones, brick, or tile. They typically extend only a short distance below the water table. Driven wells are constructed by driving small-diameter pipe into saturated unconsolidated sand and gravel. Driven wells typically are deeper than dug wells but are still relatively shallow. Most modern wells are drilled using truck-mounted machines and rotary or percussion methods. Drilled wells may be several hundred to more than a thousand feet deep, and can penetrate consolidated sediment and bedrock. Drilled wells in unconsolidated sediment have a well casing and a well screen to prevent collapse of the surrounding rock and sediment into the well. Drilled wells in bedrock typically are cased through the overlying soil and thin sediment and are open holes below. Domestic wells typically pump water from shallower depths than public-supply wells.
Interested in the water quality of public-supply wells?
Information on USGS studies of the deep wells that supply the water used by most of us for drinking can be found here.
Explore these topics related to groundwater quality
- Arsenic
- Chloride and salinity
- Corrosivity
- Groundwater age dating
- Hydraulic fracturing
- Metals
- Nutrients
- Pesticides
- Radionuclides
- Oxidation/reduction (redox)
- Surface-water/groundwater interaction
- Volatile organic compounds
Follow the links below to web pages that describe USGS science on these groundwater-quality topics.
Public Supply Wells
Groundwater Quality Research
Groundwater/Surface-Water Interaction
Rapid Fluctuations in Groundwater Quality
Predicting Groundwater Quality in Unmonitored Areas
Factors Affecting Vulnerability of Public-Supply Wells to Contamination
- Overview
More than 43 million people—about 15 percent of the U.S. population—rely on domestic (private) wells as their source of drinking water. The quality and safety of water from domestic wells are not regulated by the Federal Safe Drinking Water Act or, in most cases, by state laws. Instead, individual homeowners are responsible for maintaining their domestic well systems and for monitoring water quality.
Featured: 3-D Models of As and Mn in the Glacial Aquifer System
New 3-D models from the USGS National Water Quality Program predict where high concentrations of arsenic and manganese likely occur in the glacial aquifer system, groundwater supply for 30 million. Redox conditions and pH are controlling factors.
Featured Study: Lithium in the Nation's Groundwater
Got lithium? A new USGS study reports that about 45% of public-supply wells and about 37% of U.S. domestic supply wells have concentrations of lithium that could present a potential human-health risk.
Sources/Usage: Public Domain.Domestic supply well. Photo from USGS circular 1354 "Water Quality in the Principal Aquifers of the Piedmont, Blue Ridge, and Valley and Ridge Regions, Eastern United States, 1993 - 2009." The USGS National Water Quality Program investigates the quality of water pumped from domestic wells across the United States. These wells are the sole source of drinking water and water for other household needs for most people in many rural areas. Health risks associated with contaminants in domestic well water include gastrointestinal illness related to bacteria and other pathogens and exposure to elevated concentrations of nitrate, arsenic, radon, lead, and organic compounds. Typically, the water supplied by domestic wells is not routinely tested. As a result, people using domestic-supply wells could be drinking water with elevated concentrations of some contaminants.
The quality and safety of water from privately owned domestic wells is not regulated under Federal or, in most cases, state laws. Homeowners are primarily responsible for maintaining their domestic well systems and for any water-quality monitoring. Federal regulations under the Safe Drinking Water Act (SDWA) for public water supplies, although not directly applicable to the regulation of domestic wells, provide useful concentration benchmarks for evaluating the quality of water from domestic wells in a human-health context.
Water Quality of Domestic Wells
In a study of 2,100 domestic wells, water pumped from about one in five wells 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.
-
The contaminants most often found at these elevated concentrations were inorganic chemicals, such as metals, radionuclides, and nitrate; all of these but nitrate are derived primarily from natural sources.
-
Man-made organic compounds, such as pesticides and solvents, were detected in more than half (60 percent) of the domestic wells sampled, but concentrations were seldom greater than human-health benchmarks (less than 1 percent of wells).
-
About half of the wells had at least one “nuisance” contaminant—a compound that impairs taste, odor, or other aesthetic considerations—at a level or concentration outside the range of values recommended by the U.S. Environmental Protection Agency.
-
Microbial contaminants (for example, bacteria) were detected in about one-third of the approximately 400 wells that had their water analyzed for those contaminants.
-
Contaminants found in domestic wells 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.
More information on the quality of water from domestic wells is provided in USGS publications that summarize the quality of water in Principal Aquifers in nine regions of the United States and specifically groundwater tapped by domestic wells in Principal Aquifers.
Where Are Domestic Wells Used?
Sources/Usage: Public Domain.Map showing the number of people using domestic supply wells per square kilometer. USGS maps show where people across the Nation rely on private wells for their drinking water. The maps estimate the number of people using private wells in a given area, but individual wells are not identified. The maps can help determine where focused groundwater-quality testing or further studies are needed to help ensure safe drinking water from private wells. For instance, overlaying information on private well use with a map of potentially corrosive groundwater could be used to focus water-quality testing for lead in areas with a high density of private wells and a high likelihood of potentially corrosive groundwater.
Sources/Usage: Public Domain.Differences in well construction for domestic-supply and public-supply wells (Image is from USGS Circular 1352). Types of Domestic Wells
There are several types of domestic wells used by homeowners. The oldest wells were dug by hand. These wells typically are shallow and of large diameter (several feet), and may be lined with stones, brick, or tile. They typically extend only a short distance below the water table. Driven wells are constructed by driving small-diameter pipe into saturated unconsolidated sand and gravel. Driven wells typically are deeper than dug wells but are still relatively shallow. Most modern wells are drilled using truck-mounted machines and rotary or percussion methods. Drilled wells may be several hundred to more than a thousand feet deep, and can penetrate consolidated sediment and bedrock. Drilled wells in unconsolidated sediment have a well casing and a well screen to prevent collapse of the surrounding rock and sediment into the well. Drilled wells in bedrock typically are cased through the overlying soil and thin sediment and are open holes below. Domestic wells typically pump water from shallower depths than public-supply wells.
Interested in the water quality of public-supply wells?
Information on USGS studies of the deep wells that supply the water used by most of us for drinking can be found here.
Explore these topics related to groundwater quality
- Arsenic
- Chloride and salinity
- Corrosivity
- Groundwater age dating
- Hydraulic fracturing
- Metals
- Nutrients
- Pesticides
- Radionuclides
- Oxidation/reduction (redox)
- Surface-water/groundwater interaction
- Volatile organic compounds
-
- Science
Follow the links below to web pages that describe USGS science on these groundwater-quality topics.
Public Supply Wells
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...Groundwater 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.Groundwater/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.Rapid 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?Predicting 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.Factors 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... - Data
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