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Circular 1332

National Water-Quality Assessment Program

Quality of Water from Domestic Wells in Principal Aquifers of the United States, 1991–2004
Overview of Major Findings

By Leslie A. DeSimone, Pixie A. Hamilton, and Robert J. Gilliom

Summary of Major Findings and Implications

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More than 43 million people—about 15 percent of the U.S. population—rely on domestic wells as their source of drinking water (Hutson and others, 2004). The quality and safety of water from domestic wells, also known as private wells, are not regulated by the Federal Safe Drinking Water Act or, in most cases, by state laws. Rather, individual homeowners are responsible for maintaining their domestic well systems and for monitoring water quality. The lack of regular monitoring of domestic wells makes periodic assessments at national, regional, and local scales important sources for providing information about this key source of drinking water.

This study from the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) assesses water-quality conditions for about 2,100 domestic wells. The sampled wells are located in 48 states and in parts of 30 regionally extensive aquifers used for water supply in the United States. As many as 219 properties and contaminants, including pH, major ions, nutrients, trace elements, radon, pesticides, and volatile organic compounds (VOCs), were measured. Fecal indicator bacteria and additional radionuclides were analyzed for a smaller number of wells. The large number of contaminants assessed and the broad geographic coverage of the present study provides a foundation for an improved understanding of the quality of water from the major aquifers tapped by domestic supply wells in the United States.

Revised November 2009

First posted March 20, 2009

For additional information contact:
Massachusetts Water Science Center
U.S. Geological Survey
10 Bearfoot Road, Northborough, MA 01532

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Suggested citation:

DeSimone, L.A., Hamilton, P.A., Gilliom, R.J., 2009, Quality of water from domestic wells in principal aquifers of the United States, 1991–2004—Overview of major findings: U.S. Geological Survey Circular 1332, 48 p.


Summary of Major Findings and Implications


NAWQA’s Approach to Assessing the Quality of Water from Domestic Wells

Major Findings

More than one in five (23 percent) domestic wells contained one or more contaminants at a concentration greater than a human-health benchmark

Contaminants most often found at concentrations greater than human-health benchmarks were inorganic chemicals, with all but nitrate derived primarily from natural sources

Nitrate is the only contaminant derived primarily from man-made sources that was found at concentrations greater than a human-health benchmark in more than 1 percent of wells

Man-made organic compounds were detected in more than half (60 percent) of the sampled wells, but concentrations were seldom greater than human-health benchmarks (less than 1 percent of wells)

Microbial contaminants were detected in as many as one-third of the approximately 400 wells sampled

About half (48 percent) of the sampled wells contained at least one contaminant at a level or concentration outside the range of values recommended by USEPA for the aesthetic quality of water

Contaminants usually co-occurred with other contaminants as mixtures

References Cited

Abbreviations, Acronyms, and Units of Measure

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