Well water in Kern County, California
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Testing strongly recommended
tested well samples in Kern County exceeded the EPA limit for arsenic (10 ug/L), based on public data from USGS Water Quality Portal.
21,320 test results across 15 contaminants from at least 1,635 wells, 1909 to 2026; nitrate has the most at 3,942. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 22,694 people in Kern County get their drinking water from a private well, per USGS 2015 county water use. That is about 3% of residents.
Separately, the USGS national arsenic model estimates that 16% of the 22,694 people on private wells in Kern County draw water above 10 ug/L (the model's range is 13% to 20%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Kern County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Above limit | Samples | Detected | Median | Highest | Limit |
|---|---|---|---|---|---|---|
| Arsenic 1964 to 2026 | 1,112 | 93% | 5 | 4,000 | 10 ug/L EPA limit | |
| Uranium 1989 to 2026 | 645 | 89% | 4.09 | 2,500 | 30 ug/L EPA limit | |
| Nitrate 1917 to 2026 | 3,942 | 85% | 1.2 | 911 | 10 mg/L EPA limit | |
| Radium (226 + 228) 2006 to 2022 | 574 | 74% | 0.15 | 34 | 5 pCi/L EPA limit | |
| E. coli 2006 to 2015 | 26 | 4% | 0 | 1 | 0 MPN/100mL EPA limit | |
| Fluoride 1946 to 2026 | 2,818 | 97% | 0.6 | 150 | 4 mg/L EPA limit | |
| PFOS 2021 to 2024 | 65 | 3% | 0 | 8.7 | 4 ng/L EPA limit | |
| Lead 1968 to 2026 | 667 | 23% | 0 | 40 | 15 ug/L EPA limit | |
| Copper 1966 to 2026 | 886 | 45% | 0 | 5.6 | 1.3 mg/L EPA limit | |
| PFOA 2021 to 2024 | 65 | 2% | 0 | 3.5 | 4 ng/L EPA limit | |
| Chloride 1909 to 2026 | no limit | 3,380 | 100% | 60 | 55,800 | 250 mg/L nuisance level |
| Sodium 1909 to 2026 | no limit | 3,202 | 100% | 90.0 | 36,300 | 20 mg/L health guideline |
| Iron 1917 to 2026 | no limit | 2,282 | 77% | 20 | 400,000 | 300 ug/L nuisance level |
| Manganese 1945 to 2026 | no limit | 1,561 | 75% | 2.74 | 20,700 | 300 ug/L health guideline |
| Radon 1995 to 2018 | no limit | 95 | 100% | 540 | 4,670 | 2,000 pCi/L health guideline |
Over time
Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.
| Contaminant | before 2000 | 2000s | 2010s | 2020s |
|---|---|---|---|---|
| Nitrate | 12%2,622 samples | 9%316 samples | 11%437 samples | 18%567 samples |
| Fluoride | 3%2,169 samples | 0%141 samples | <1%220 samples | 0%288 samples |
| Arsenic | 41%438 samples | 25%173 samples | 30%210 samples | 26%291 samples |
| Copper | <1%388 samples | 0%91 samples | 0%172 samples | 0%235 samples |
| Lead | <1%184 samples | 0%91 samples | 0%171 samples | 0%221 samples |
| Uranium | 63%82 samples | 2%98 samples | 15%183 samples | 8%282 samples |
Nitrate above the limit in Kern County rose from 11% of 437 samples in the 2010s to 18% of 567 in the 2020s.
Uranium above the limit in Kern County fell from 15% of 183 samples in the 2010s to 8% of 282 in the 2020s.
Fluoride, arsenic, copper, lead have held within a few points between the two most recent periods with enough samples.
Closer than the county
See the sampled wells near your address
The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.
Check my addressWhat this means
The contaminants most often above their limit here are arsenic (32% of 1,112 samples), uranium (16% of 645 samples), and nitrate (13% of 3,942 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Iron, and Manganese are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Kern County
- 1Arsenic32% of 1,112 local samples were above the limit.
- 2Uranium16% of 645 local samples were above the limit.
- 3Nitrate13% of 3,942 local samples were above the limit.
- 4Radium (226 + 228)5% of 574 local samples were above the limit.
- 5E. coli4% of 26 local samples were above the limit.
- 6Fluoride2% of 2,818 local samples were above the limit.
- 7PFOS2% of 65 local samples were above the limit.
- 8Volatile organic compounds (VOCs)1,057 leaking underground storage tank sites on record locally.
- 9Metals panel39 hazardous waste sites on record locally.
Test your Kern County well for arsenic, uranium and nitrate
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.
Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.
Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.
Where to get a well tested in California: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Kern County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Kern County
Central Valley aquifer system
Unconsolidated sand and gravel. Wells in sand and gravel are usually shallow and productive, and they recharge quickly from the surface. That makes them the most exposed to nitrate, bacteria and anything spilled nearby, and the least likely to carry arsenic or radon from the rock.
Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.
Official help in California
Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.
- GAMA - Well Owners, State Water Resources Control Board
- Environmental Laboratory Accreditation Program (ELAP), State Water Resources Control Board
Contamination sources on record in Kern County
California GeoTracker and EnviroStor sites records 1,057 leaking underground storage tank sites and 39 hazardous waste sites in Kern County, among 2,225 regulated sites in total. Groundwater does not follow property lines, so a well within a few hundred feet of one of these is worth testing for what that site could release.
- 1,057
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 39
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 71
- lined landfills and transfer facilities
- 1,058
- other remediation projects
Treatment that fits the local profile
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Uranium
Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
E. coli
Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Systems we would look at first
Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For arsenic
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For arsenic
Whole-house arsenic and uranium filter
whole-house, at the point of entry, about $2,500
Adsorptive iron-based media; sized to your well yield.
For arsenic
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
For E. coli
UV disinfection system
whole-house, at the point of entry, about $900
Fix the well cap and casing first; UV keeps bacteria from returning.
For E. coli
Aquasana Rhino Well Water with UV
whole-house, at the point of entry, about $2,871
Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.
Free, no obligation
Get on the list for a free in-home water test in Kern County
No water treatment company serves Kern County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Kern County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Kern County?
Arsenic was detected in 93% of 1,112 public well samples in Kern County, and 32% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Kern County?
The median radon level across 95 public samples in Kern County was 540 pCi/L, with a high of 4,670 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Kern County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Counties near Kern County
Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.
Want the numbers themselves? Download the California dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 21,320 samples in Kern County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 22,694 people on private wells in Kern County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 2026.
- California GeoTracker and EnviroStor sites: 2,225 regulated sites located in Kern County. Leaking underground storage tank and cleanup sites from the State Water Board GeoTracker export on data.ca.gov, and DTSC EnviroStor cleanup sites. Retrieved September 15, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.