Well water in Medina County, Texas
In Medina County, 4% of 504 tested well samples exceeded the EPA limit for fluoride (4 mg/L), based on public data from USGS Water Quality Portal and Texas Water Development Board Groundwater Database.
The strongest signal is E. coli: 6% of 16 local samples were above the limit, too few samples to carry the headline but first on the test list below.
4,537 test results across 16 contaminants from at least 258 wells, 1930 to 2026; nitrate has the most at 796. Data refreshed September 15, 2026.
Compiled by Nick at Well Water Nerd from public records. How these pages are built
TWDB samples an ambient monitoring network of wells on a rotation, so these describe aquifers, not a survey of homeowners' tests.
An estimated 4,730 people in Medina County get their drinking water from a private well, per USGS 2015 county water use. That is about 10% of residents.
Separately, the USGS national arsenic model estimates that 2% of the 4,730 people on private wells in Medina County draw water above 10 ug/L (the model's range is 1% to 2%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Medina 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 |
|---|---|---|---|---|---|---|
| E. coli 2008 to 2018 | 16 | 6% | 0 | 5 | 0 MPN/100mL EPA limit | |
| Fluoride 1930 to 2026 | 504 | 96% | 0.2 | 5.9 | 4 mg/L EPA limit | |
| Radium (226 + 228) 1990 to 2018 | 60 | 82% | 0.31 | 10.7 | 5 pCi/L EPA limit | |
| Nitrate 1930 to 2026 | 796 | 94% | 1.2 | 220 | 10 mg/L EPA limit | |
| Arsenic 1972 to 2026 | 354 | 36% | 0 | 2 | 10 ug/L EPA limit | |
| Copper 1970 to 2026 | 343 | 73% | 0.001 | 0.062 | 1.3 mg/L EPA limit | |
| Lead 1972 to 2026 | 333 | 47% | 0 | 7.1 | 15 ug/L EPA limit | |
| Uranium 1996 to 2026 | 85 | 62% | 0.619 | 5.31 | 30 ug/L EPA limit | |
| Chloride 1930 to 2026 | no limit | 656 | 100% | 13.9 | 5,500 | 250 mg/L nuisance level |
| Sodium 1930 to 2026 | no limit | 544 | 100% | 7.55 | 2,080 | 20 mg/L health guideline |
| Iron 1930 to 2026 | no limit | 398 | 46% | 0 | 5,271 | 300 ug/L nuisance level |
| Manganese 1959 to 2026 | no limit | 389 | 29% | 0 | 3,000 | 300 ug/L health guideline |
| Radon 1996 to 2017 | no limit | 36 | 64% | 105 | 2,010 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: Gross alpha (7), 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 |
|---|---|---|---|---|
| Nitrate | 3%559 samples | 2%89 samples | 3%107 samples | 0%41 samples |
| Fluoride | 5%371 samples | 4%57 samples | 0%54 samples | 0%22 samples |
| Arsenic | 0%272 samples | 0%56 samples | 0%17 samples | n/a |
| Copper | 0%260 samples | 0%57 samples | 0%17 samples | n/a |
| Lead | 0%250 samples | 0%57 samples | 0%17 samples | n/a |
| Uranium | 0%26 samples | 0%33 samples | 0%17 samples | n/a |
Nitrate, fluoride, 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 e. coli (6% of 16 samples), fluoride (4% of 504 samples), and radium (226 + 228) (3% of 60 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 is widespread in local groundwater. It is mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Medina County
- 1E. coli6% of 16 local samples were above the limit.
- 2Fluoride4% of 504 local samples were above the limit.
- 3Radium (226 + 228)3% of 60 local samples were above the limit.
- 4Nitrate3% of 796 local samples were above the limit.
- 5RadonMedian local reading is 105 pCi/L.
- 6Gross alphaAbove the limit in 1 of 7 local samples; too few to quote a rate.
- 7ChlorideDetected in 100% of local samples.
- 8Volatile organic compounds (VOCs)51 leaking underground storage tank sites on record locally.
Test your Medina County well for E. coli, fluoride and radium (226 + 228)
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 Texas: certified labs, state programs and prices.
Already have results back? Get your lab report read against the Medina County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Medina County
Not a principal aquifer
The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.
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 Texas
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.
- Private Wells, Texas Groundwater Protection Committee
- Environmental Laboratory (NELAP) Accreditation, TCEQ
Contamination sources on record in Medina County
TCEQ records 51 leaking underground storage tank sites in Medina County, among 60 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.
- 51
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 9
- lined landfills and transfer facilities
Treatment that fits the local profile
E. coli
Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Fluoride
Point-of-use reverse osmosis; Activated alumina; Distillation
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
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 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.
For fluoride
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For fluoride
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.
Free, no obligation
Get on the list for a free in-home water test in Medina County
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Common questions
Is there arsenic in well water in Medina County?
Arsenic was detected in 36% of 354 public well samples in Medina County, and 0% 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 Medina County?
The median radon level across 36 public samples in Medina County was 105 pCi/L, with a high of 2,010 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Medina 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 Medina 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 Texas dataset as CSV, every county and town, with the sources named.
Sources
- USGS Water Quality Portal: 3,565 samples in Medina 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.
- Texas Water Development Board Groundwater Database: 972 samples in Medina County. Water quality samples from the Texas Water Development Board Groundwater Database, collected by TWDB, groundwater conservation districts and cooperators. Retrieved September 9, 2026.
- USGS national arsenic model (Ayotte 2017): estimated share of 4,730 people on private wells in Medina 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.
- TCEQ regulated sites: 60 regulated sites located in Medina County. Leaking petroleum storage tank sites, state Superfund sites and municipal solid waste landfills from the Texas Commission on Environmental Quality. Retrieved September 9, 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.