A compiled reference of 20 verified statistics on private well water in the United States: how many people rely on wells, the fact that no one tests that water for them, how often it carries a contaminant above a health benchmark, what the government recommends testing for and how often, and what testing costs. Every figure is drawn from a named public source (USGS groundwater assessments, EPA and CDC private-well guidance, and well-testing laboratory pricing) and independently checked before publishing.
In a USGS assessment of 6,600 wells, 22% of samples from aquifers used for drinking water contained at least one contaminant at a level of potential human-health concern. Geologic sources, mainly manganese, arsenic, and radon, accounted for about 80% of those exceedances.
Source: USGS, The Quality of the Nation's Groundwater, 1991-2010 (usgs.gov).
Key statistics
Key takeaways
Private wells sit in a regulatory blind spot: tens of millions of people, no mandatory testing, and a contamination rate that is far from negligible. The numbers below trace who is exposed, what is in the water, and what closing the gap costs.
More than 43 million Americans, about 15% of the population, rely on private wells for drinking water.
Private wells are not regulated under the Safe Drinking Water Act; the owner is responsible for testing.
About 1 in 5 wells has at least one contaminant above a human-health benchmark.
Most contaminants of concern are natural, mainly arsenic, manganese, and radon; nitrate is the main man-made one.
The CDC recommends testing at least once a year for coliform bacteria, nitrates, TDS, and pH.
A basic bacteria-and-nitrate test costs about $15 to $50; most owners spend $50 to $200 a year.
How we built this report
Every figure was compiled in September 2026 from named public sources and verified against the original before publishing.
- Compiled from primary sources
USGS national groundwater-quality assessments, EPA and CDC private-well guidance, and published well-testing laboratory pricing.
- Government data for the contamination claims
Prevalence figures come only from USGS sampling studies, read from the USGS material directly, not from vendor marketing.
- Disagreements shown, not averaged
Two USGS studies report 23% and 22%; we show both and describe each rather than blending them.
- Independent review
Written by one co-founder, reviewed by the other before publishing.
Scope note: contamination percentages are from USGS sampling studies of thousands of wells, not a census of all wells, and a contaminant "of potential health concern" means it exceeded a benchmark, not that illness occurred. Testing costs are lab and provider ranges that vary by region, panel, and whether a county offers subsidized tests. Testing frequency and what to test for should be confirmed with your state or county health department.
Private well water, by the numbers
All 20 figures, grouped into four themes, each from a named public source and independently verified against the original.
Who relies on wells, and the regulatory gap
Private wells are common and, uniquely among US drinking-water sources, unregulated. According to the EPA (epa.gov), around 15% of the US population, more than 43 million people, rely on private wells, and "the quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act nor by most state governments."
Statistic 1
Around 15% of the US population, more than 43 million people, rely on private wells for drinking water.
EPA / USGS (2026)
Statistic 2
More than 23 million households rely on private wells for drinking water.
EPA (2026)
Statistic 3
Private wells are not regulated under the Safe Drinking Water Act, nor by most states; the owner is responsible for safe water.
EPA / CDC (2026)
Statistic 4
Over 98% of private-well water in the US comes from groundwater.
USGS (2026)
What this means: A public water system is tested to federal standards on a schedule; a private well is not tested by anyone unless the owner arranges it. For a rental or vacation property on a well, that responsibility, and the liability, sits entirely with the operator.
What is in the water
The contamination rate is not trivial. According to the USGS (usgs.gov), a study of about 2,100 private wells found 23% had at least one contaminant at a level of potential health concern, and a broader assessment of 6,600 wells found 22% of samples from aquifers used for drinking water exceeded a human-health benchmark. Most of those contaminants are natural.
Statistic 5
About 23% of roughly 2,100 private wells sampled had at least one contaminant at a level of potential health concern.
USGS (2026)
Statistic 6
In a USGS assessment of 6,600 wells (1991-2010), 22% of samples from aquifers used for drinking water exceeded a human-health benchmark.
USGS, Quality of the Nation's Groundwater
Statistic 7
Geologic-source contaminants, mainly manganese, arsenic, and radon, accounted for about 80% of the concentrations that exceeded a health benchmark.
USGS (2026)
Statistic 8
Nitrate exceeded its health benchmark in about 4% of wells, the only man-made constituent above 1% of samples.
USGS (2026)
Statistic 9
High nitrate usually comes from man-made sources like septic tanks or fertilizer, especially in agricultural areas.
USGS (2026)
Statistic 10
The contaminants most often found at health-concern levels are radon, arsenic, uranium, manganese, and nitrate.
USGS (2026)
What this means: Because most well contamination is geologic, it is invisible, tasteless, and specific to the aquifer, which means a clean-tasting well tells you nothing. The nitrate exception ties well safety directly to nearby septic systems and farming, the same on-site infrastructure a property inspection already covers.
What to test, and how often
Because no agency does it for well owners, the CDC lays out a baseline. According to the CDC (cdc.gov), owners should "test your well water at least once every year for total coliform bacteria, nitrates, total dissolved solids, and pH level," with additional tests based on local conditions, and it reiterates that "government officials do not regulate, treat, or monitor tap water from private wells."
Statistic 11
The CDC recommends testing private well water at least once a year for total coliform bacteria, nitrates, total dissolved solids, and pH.
CDC (2026)
Statistic 12
Additional testing (for contaminants such as arsenic, radon, or metals) is recommended based on local conditions.
CDC (2026)
Statistic 13
The government does not regulate, treat, or monitor water from private wells; the well owner is solely responsible.
CDC (2026)
What this means: The annual baseline, coliform and nitrate, is cheap and catches the two fastest-changing risks (bacterial intrusion and septic or fertilizer runoff). The slower geologic risks warrant a broader panel at purchase and periodically after.
What testing costs
Testing is inexpensive relative to the risk it covers. According to well-testing laboratories, a basic bacteria test runs about $15 to $50 and a nitrate test $20 to $40 (welldrillingcost.com), a basic homeowner panel about $75 to $150, and a comprehensive 50-plus-parameter panel $200 to $500 (etrlabs.com). Many county health departments offer subsidized coliform and nitrate tests.
Statistic 14
A basic bacteria (coliform/E. coli) test costs about $15 to $50.
Well Drilling Cost (2026)
Statistic 15
A nitrate/nitrite test costs about $20 to $40.
Well Drilling Cost (2026)
Statistic 16
A basic homeowner panel (bacteria, nitrate, pH, hardness, iron) costs about $75 to $150.
ETR Labs (2026)
Statistic 17
A standard panel adding lead, arsenic, manganese, and TDS costs about $150 to $300.
ETR Labs (2026)
Statistic 18
A comprehensive panel testing 50-plus parameters costs about $200 to $500.
Well Drilling Cost (2026)
Statistic 19
A heavy-metals test (lead, arsenic, and others) costs about $50 to $150.
Well Drilling Cost (2026)
Statistic 20
Most homeowners spend about $50 to $200 per year on well water testing.
Well Drilling Cost / ETR Labs (2026)
What this means: At $15 to $50 for the annual baseline, testing is one of the cheapest risk controls a property owner has, far below the cost of the septic, plumbing, or filtration work that a bad result would trigger. The cost is not the barrier; remembering to do it, and recording that it was done, is.
Cite this study
Academic or press use: copy a ready-made reference. RapidEye is the publisher.
Quick FAQ
How often should you test private well water?
The CDC recommends testing private well water at least once every year for total coliform bacteria, nitrates, total dissolved solids, and pH, with additional tests based on local conditions (cdc.gov). Private wells are not regulated by the EPA under the Safe Drinking Water Act, so the well owner is responsible for testing.
How common is contamination in private wells?
About 1 in 5 private wells contains at least one contaminant at a level of potential health concern (usgs.gov). A USGS study of about 2,100 wells found 23% had such a contaminant, and a broader USGS assessment of 6,600 wells found 22% of samples from aquifers used for drinking water exceeded a human-health benchmark, mostly natural contaminants like arsenic, manganese, and radon.
How much does well water testing cost?
A basic bacteria (coliform) test costs about $15 to $50 and a nitrate test $20 to $40 (welldrillingcost.com). A basic homeowner panel runs about $75 to $150, a standard panel with metals $150 to $300, and a comprehensive 50-plus-parameter panel $200 to $500 (etrlabs.com). Most homeowners spend $50 to $200 per year, and many counties offer subsidized coliform and nitrate tests.
Are private wells regulated?
No. Private wells are not regulated by the federal government under the Safe Drinking Water Act, nor by most state governments (epa.gov). Around 15% of the US population, more than 43 million people, rely on private wells, and each owner is responsible for testing and treating their own water.
Data sources
Every figure traces to one of these named public sources, each checked against the original before publishing. We name each source and show its root domain, but do not hyperlink external sources; internal links stay live.
U.S. Geological SurveyNational groundwater-quality and private-well contamination assessmentsusgs.gov
U.S. Environmental Protection AgencyPrivate drinking water wells guidanceepa.gov
Centers for Disease Control and PreventionGuidelines for testing well watercdc.gov
Well Drilling CostWell water testing cost guidewelldrillingcost.com
ETR LabsWell water testing cost breakdownetrlabs.com