About 0% of the county's 763,623 residents. Rank 82 of 120 in Kentucky.
95% range 150 to 249 private-well users (2010 base year). Rank 9 of 120 in Kentucky.
Highest potential (average indoor radon may be greater than 4 pCi/L). EPA says the map should not be used to decide whether an individual home needs testing.
Labs with an address in this county, from the official state lists on this site, matched by ZIP code.
What to test for in Jefferson County
Private wells are not regulated like public water: EPA advises owners to test their well every year for total coliform bacteria, nitrates, total dissolved solids and pH. Your state's own schedule:
- The Kentucky Division of Water says well owners should have their well water tested every year for bacteria. It lists other reasons to test: a change in the water's taste, odor or appearance, recurring stomach illness in the household, a pregnancy or new infant in the home, a dangerous contaminant in a neighbor's water, and checking how well home treatment equipment works. source
Arsenic. USGS estimates that about 194 people using private wells in Jefferson County had arsenic above 10 µg/L, EPA's limit for public water (2010 base year; 95% range 150 to 249). USGS describes this kind of estimate as useful "for broad screening of the population at risk", so it says nothing certain about any one well. Arsenic has no taste or smell: test for it by name.
Radon. EPA puts Jefferson County in Zone 1: highest potential (average indoor radon may be greater than 4 pCi/L). That map is about radon in indoor air, and EPA says it should not be used to decide whether an individual home needs testing. If radon is found in your air and you have a well, EPA suggests testing the water too: see radon in well water.
For anything specific to your home (farms nearby, old plumbing, a new baby, a smell or stain), use the which-tests checklist. When the results arrive, check your numbers against EPA's limits.
Show the numbers
| Item | Value | Note |
|---|---|---|
| Pike County | 1,348 people (2010 base year) | |
| Bullitt County | 421 people (2010 base year) | |
| Oldham County | 421 people (2010 base year) | |
| Lawrence County | 355 people (2010 base year) | |
| Letcher County | 326 people (2010 base year) | |
| Jefferson County (this county) | 194 people (2010 base year) |
USGS model estimate for broad screening, not a measurement of any well. Only a test tells you about your own well. Source: USGS, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter (Ayotte, Medalie and Qi, 2017), accessed 2026-11-01.
PFAS in public water near Jefferson County (public supply, not your well)
This is public water data, not your well. A private well draws its own groundwater, which can have more or less PFAS than the public supply nearby. Only a test of your well tells you.
Under EPA’s fifth Unregulated Contaminant Monitoring Rule (UCMR 5), public water systems sampled their water for 29 PFAS between Jan 3, 2023 and Jun 17, 2026. 4 public systems that serve ZIP codes mainly in Jefferson County reported results. 4 of them had at least one sample with PFOA or PFOS at or above 4.0 ng/L, and 4 had at least one of the 29 PFAS measured at or above its reporting level.
| Public water system | System ID | Highest PFOA (ng/L) | Highest PFOS (ng/L) |
|---|---|---|---|
| Louisville Water Company | KY0560258 | 7.5 | |
| Mt Washington Water Company | KY0150300 | 7.2 | |
| Taylorsville Water Works | KY1080425 | 6.5 | |
| West Shelby Water District | KY1060457 | 4.6 |
4.0 ng/L (parts per trillion) is both EPA’s UCMR 5 reporting level for PFOA and PFOS and the number in EPA’s 2024 limit for public water. That limit is judged on a running annual average, so one sample at that level is not a violation. EPA proposed changes to its PFAS rules in May 2026: see PFAS in well water for the current status and who should test a well. To test your own well, find a lab certified for PFAS.
Method: a system counts for this county when it reports serving a ZIP code whose largest land part is in this county, so a system serving several counties counts in each. Source: U.S. EPA, UCMR 5 occurrence data (by state), file dated Oct 15, 2026; downloaded Nov 1, 2026.
Testing programs and help in Kentucky
- To find out which contaminants may be of local concern (some, such as arsenic and radon, are area specific), the Division of Water suggests contacting the Division of Water or Division of Waste Management, a certified drinking water testing lab, a qualified local well contractor or treatment company, or local health or environmental health officials. source
- If you are concerned about PFAS in your well, Kentucky's Department for Environmental Protection suggests contacting a certified laboratory about testing; it posts a list of certified PFAS labs at eec.ky.gov/PFAS and notes that PFAS testing can be expensive. source
Buying a home with a well in Jefferson County
Loan test (FHA, VA, USDA) in Jefferson County, KY
- VA. Test results are valid for 90 days from the date the local health authority certifies them, unless the local authority says otherwise. VA’s chapter names no list of contaminants: the water must meet the local health authority’s requirements, or EPA guidelines where it has none. Your lender may ask for specific tests.
- FHA. A well test is required in the situations FHA’s handbook lists, among others, and the report may not be more than 180 days old at disbursement.
- USDA. Guaranteed loans need a water quality test for a private well, done by the local health authority or a state-certified lab, and no more than 180 days old at closing.
Lenders can ask for more (extra tests, a particular lab, who takes the sample): ask your lender before you book. Federal rules as read on Nov 3, 2026 source 1 source 2 source 3. Full comparison: VA, FHA and USDA well water test requirements. Loan test kits sold by mail, with price and days to results: kits compared.
State-certified labs in Jefferson County
Beckmar Environmental Laboratory
3251 Ruckriegel Parkway, Louisville, KYPublic samples: ask the labMicrobac Laboratories, Inc.-KTL
3323 Gilmore Industrial Blvd, Louisville, KYPublic samples: ask the labSee all Kentucky labs in the finder and filter by the test you need and by labs that take homeowner samples.
- USGS, Estimated use of water in the United States, county-level data for 2015 (Dieter et al., ver. 2.0, 2018)
- USGS, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter (Ayotte, Medalie and Qi, 2017)
- U.S. EPA, Map of Radon Zones, county list (EPA 402/A-16/001)
- U.S. Census Bureau, 2020 ZCTA to county relationship file (lab ZIP codes to counties)
- 2026 KY Certified Drinking Water PFAS Laboratory List (Revised 1/23/2026)
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