Well water in Ventura County, California
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Testing recommended
tested well samples in Ventura County exceeded the EPA limit for nitrate (10 mg/L), based on public data from USGS Water Quality Portal.
4,413 test results across 15 contaminants from at least 308 wells, 1933 to 2022; chloride has the most at 1,029. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
An estimated 18,303 people in Ventura County get their drinking water from a private well, per USGS 2015 county water use. That is about 2% of residents.
Separately, the USGS national arsenic model estimates that 7% of the 18,303 people on private wells in Ventura County draw water above 10 ug/L (the model's range is 5% to 9%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Ventura 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 |
|---|---|---|---|---|---|---|
| Nitrate 1952 to 2022 | 495 | 57% | 0.1 | 168 | 10 mg/L EPA limit | |
| Arsenic 1978 to 2022 | 162 | 85% | 0.535 | 11.9 | 10 ug/L EPA limit | |
| Fluoride 1952 to 2022 | 577 | 97% | 0.4 | 8.8 | 4 mg/L EPA limit | |
| Copper 1978 to 2022 | 73 | 19% | 0 | 0.013 | 1.3 mg/L EPA limit | |
| Lead 1978 to 2022 | 71 | 28% | 0 | 3.24 | 15 ug/L EPA limit | |
| Uranium 2007 to 2022 | 69 | 94% | 3.99 | 26.8 | 30 ug/L EPA limit | |
| Radium (226 + 228) 2007 to 2017 | 46 | 89% | 0.29 | 0.89 | 5 pCi/L EPA limit | |
| Chloride 1933 to 2022 | no limit | 1,029 | 100% | 68 | 24,000 | 250 mg/L nuisance level |
| Sodium 1933 to 2022 | no limit | 632 | 100% | 118 | 13,000 | 20 mg/L health guideline |
| Iron 1966 to 2022 | no limit | 632 | 84% | 41 | 33,000 | 300 ug/L nuisance level |
| Manganese 1972 to 2022 | no limit | 592 | 90% | 62 | 8,400 | 300 ug/L health guideline |
| Radon 2007 to 2011 | no limit | 10 | 100% | 565 | 1,180 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (9), PFOS (8), PFOA (8).
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 |
|---|---|---|---|---|
| Fluoride | <1%482 samples | 0%56 samples | 0%31 samples | n/a |
| Nitrate | 14%405 samples | 16%51 samples | 13%31 samples | n/a |
| Arsenic | 0%15 samples | <1%108 samples | 0%31 samples | n/a |
| Copper | n/a | 0%31 samples | 0%30 samples | n/a |
| Lead | n/a | 0%31 samples | 0%30 samples | n/a |
| Uranium | n/a | 0%31 samples | 0%30 samples | n/a |
Fluoride, nitrate, arsenic, copper, lead, uranium 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 nitrate (14% of 495 samples), arsenic (<1% of 162 samples), and fluoride (<1% of 577 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 Ventura County
- 1Nitrate14% of 495 local samples were above the limit.
- 2Arsenic<1% of 162 local samples were above the limit.
- 3Fluoride<1% of 577 local samples were above the limit.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5RadonMedian local reading is 565 pCi/L.
- 6ChlorideDetected in 100% of local samples.
- 7ManganeseDetected in 90% of local samples.
- 8Volatile organic compounds (VOCs)1,491 leaking underground storage tank sites on record locally.
- 9Metals panel16 hazardous waste sites on record locally.
Test your Ventura County well for nitrate, arsenic and fluoride
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 Ventura County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
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 Ventura County
California GeoTracker and EnviroStor sites records 1,491 leaking underground storage tank sites and 16 hazardous waste sites in Ventura County, among 2,179 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.
- 1,491
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 16
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 82
- lined landfills and transfer facilities
- 590
- other remediation projects
Treatment that fits the local profile
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
Chloride
Point-of-use reverse osmosis; Distillation
Manganese
Oxidizing filter (greensand, birm) whole-house; Water softener (low levels); Point-of-use reverse osmosis
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 nitrate
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For nitrate
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 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 iron
Iron and manganese oxidizing filter
whole-house, at the point of entry, about $1,800
Air-injection or greensand media; fixes staining at the source.
Free, no obligation
Get on the list for a free in-home water test in Ventura County
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Common questions
Is there arsenic in well water in Ventura County?
Arsenic was detected in 85% of 162 public well samples in Ventura County, and <1% 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 Ventura County?
The median radon level across 10 public samples in Ventura County was 565 pCi/L, with a high of 1,180 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Ventura 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 Ventura 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: 4,413 samples in Ventura 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 18,303 people on private wells in Ventura 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: 2,179 regulated sites located in Ventura 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.