DuPage County Well Water Testing
Private-well guidance for DuPage County, Illinois: USGS area-risk estimates for arsenic and nitrate, a recommended test panel, and how to get your own well tested at a Illinois-certified lab.
DuPage County groundwater risk (area estimates)
These are modeled USGS estimates for the county area — not a measurement of your specific well.
Arsenic
area estimate5%
modeled chance a well in this area exceeds 10 µg/L (the EPA limit).
19% chance of exceeding 5 µg/L.
Most-probable concentration category: <=5 ug/L.
Nitrate
area estimate0.02 mg/L
predicted nitrate (as N) for domestic-supply depth.
This estimate is below the 10 mg/L EPA limit, but individual wells can still exceed it.
Private wells
area estimate64,010
people on private wells in DuPage County.
Roughly 25,604 households, estimated from the USGS modeled domestic-supply population.
Area context
Additional state-only or optional layers for DuPage County, shown where the data exists.
Uranium
area estimateA state-only uranium model is not available for Illinois. See observed samples and test your own well to learn its uranium level.
Radon
area estimateA state-only radon model is not available for Illinois. See observed samples and test your own well to learn its radon level.
Primary aquifer
area contextWells in DuPage County most likely draw from the Silurian-Devonian aquifers (USGS national aquifer code 410). This is the dominant principal aquifer mapped under the county area, not a determination for any single well.
Agricultural land use
area contextAbout 2% of the DuPage County area is row-crop farmland (USDA Cropland Data Layer). Intensively farmed row-crop land raises the likelihood of elevated nitrate in nearby groundwater, so it is a reason to include nitrate in your test panel. This is land-use context for the county area — not a measurement of nitrate in any well.
PFAS
public-system proxyPFAS were detected in 4 of 34 public water systems tested in DuPage County under the EPA's national PFAS monitoring program (UCMR5).
This reflects PFAS detections in public water systems near DuPage County — a regional proxy, not a measurement of private wells. If you rely on a private well, only a lab test of your own water reveals its PFAS level.
These figures are USGS area estimates: statistical groundwater models describing how likely elevated contaminant levels are across a county. They are not designed to predict the concentration in any single well. Only testing your own well reveals its water quality.
Recommended test panel for DuPage County
- coliform
Coliform bacteria is recommended for every private well as the universal baseline test. The federal loan minimum (FHA, VA, USDA) tests for coliform, nitrate, nitrite, lead.
Federal FHA, VA, and USDA home loans require testing for coliform, nitrate, nitrite, lead at the point of a federally-backed loan. See the program-specific rules: FHA well test, VA well test, USDA well test.
Already have lab results? Interpret your well water test results to see how your own numbers compare to EPA limits.
How DuPage County compares across Illinois
Where DuPage County's modeled area estimates sit relative to the other Illinois counties in our analysis.
- Arsenicbelow the Illinois median
DuPage County: 5% · Illinois median: 8% · flagged in 45 of 102 counties.
See all Illinois arsenic data → - Nitratebelow the Illinois median
DuPage County: 0.02 mg/L · Illinois median: 0.29 mg/L · flagged in 0 of 102 counties.
See all Illinois nitrate data →
Municipal (public) water in DuPage County
Most DuPage County residents are served by a public water system, not a private well. If that's you, open your city's tap-water quality report:
- Naperville
- Bartlett
- Woodridge
- Elmhurst
- Downers Grove
- Wheaton
- Lombard
- Addison
- Bloomingdale
- Carol Stream
- Hanover Park
- Darien
+ 18 more — search every city.
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Find a state-certified lab
Test your DuPage County well through a lab certified by the Illinois Environmental Protection Agency (chemistry) and Illinois Department of Public Health (microbiology) — find one in the official directory (PDF lists—chemistry certifications through IEPA, microbiology through IDPH).
Recognize & research well-water problems
Notice a problem? Diagnose it by symptom
Learn about these contaminants in drinking water
Data sources
DuPage County's estimates are modeled from public federal datasets. See the data & methodology for how we build, source, and validate them.
- USGS arsenic probability-of-exceedance model
- USGS nitrate predicted concentration, domestic-supply depth
- USGS domestic (private) well population density
- USGS principal aquifers
- USDA NASS Cropland Data Layer (CDL) 30m
- EPA UCMR5 PFAS occurrence in public water systems (Fifth Unregulated Contaminant Monitoring Rule)
- EPA/USGS Water Quality Portal (waterqualitydata.us)
- US Census TIGER/Line county polygons
By TapWaterData Editorial · Last updated June 26, 2026.
DuPage County well water FAQ
How do I test my well water in DuPage County?
Order a sample kit covering the recommended panel for DuPage County (coliform), then send it to a Illinois-certified drinking-water laboratory. Certified labs use EPA-approved methods, so the results are defensible for a federally-backed home loan. You can also use a mail-in test kit for a convenient EPA-certified analysis.
What does the USGS arsenic estimate mean for my well?
It is an area estimate, not a prediction for your specific well. The USGS model describes how likely elevated arsenic is across DuPage County as a whole; an individual well in the county can be much higher or much lower. Only testing your own well reveals its actual arsenic level.
How often should a private well be tested?
The CDC recommends testing private wells at least once a year for total coliform bacteria and nitrate, and more often if you notice a change in taste, color, or odor, or after flooding or nearby construction.
Does Illinois require well testing?
Federal FHA, VA, and USDA home-loan programs require a private-well water test at the point of a federally-backed loan. A state sale, rental, or recurring testing mandate was not independently verified for this state — consult your state's program.
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