Well water in Dimmit County, Texas
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Testing recommended
tested well samples in Dimmit County exceeded the EPA limit for arsenic (10 ug/L), based on public data from Texas Water Development Board Groundwater Database and USGS Water Quality Portal.
The strongest signal is gross alpha: 12% of 17 local samples were above the limit, too few samples to carry the headline but first on the test list below.
764 test results across 14 contaminants from at least 54 wells, 1930 to 2018; chloride has the most at 126. 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 1,408 people in Dimmit County get their drinking water from a private well, per USGS 2015 county water use. That is about 13% of residents.
Separately, the USGS national arsenic model estimates that 6% of the 1,408 people on private wells in Dimmit County draw water above 10 ug/L (the model's range is 5% to 8%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Dimmit 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 |
|---|---|---|---|---|---|---|
| Gross alpha 1990 to 2014 | 17 | 59% | 2.6 | 40 | 15 pCi/L EPA limit | |
| Radium (226 + 228) 1990 to 2015 | 20 | 85% | 0.95 | 18 | 5 pCi/L EPA limit | |
| Arsenic 1990 to 2018 | 53 | 30% | 0 | 47.9 | 10 ug/L EPA limit | |
| Nitrate 1990 to 2018 | 54 | 41% | 0 | 51 | 10 mg/L EPA limit | |
| Fluoride 1965 to 2018 | 120 | 99% | 0.475 | 4.5 | 4 mg/L EPA limit | |
| Copper 1990 to 2018 | 53 | 34% | 0 | 0.057 | 1.3 mg/L EPA limit | |
| Lead 1990 to 2018 | 53 | 19% | 0 | 6.14 | 15 ug/L EPA limit | |
| Uranium 2008 to 2018 | 23 | 43% | 0 | 6.83 | 30 ug/L EPA limit | |
| Chloride 1930 to 2018 | no limit | 126 | 100% | 112 | 5,150 | 250 mg/L nuisance level |
| Sodium 1930 to 2018 | no limit | 125 | 100% | 147 | 2,250 | 20 mg/L health guideline |
| Iron 1930 to 2018 | no limit | 60 | 72% | 100 | 1,660 | 300 ug/L nuisance level |
| Manganese 1969 to 2018 | no limit | 54 | 81% | 17.6 | 552 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (3), Radon (3).
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 | 2%88 samples | 8%13 samples | 0%19 samples | n/a |
| Nitrate | 0%21 samples | 8%13 samples | 5%20 samples | n/a |
| Arsenic | 0%21 samples | 8%13 samples | 11%19 samples | n/a |
| Copper | 0%21 samples | 0%13 samples | 0%19 samples | n/a |
| Lead | 0%21 samples | 0%13 samples | 0%19 samples | n/a |
Nitrate above the limit in Dimmit County rose from 0% of 21 samples before 2000 to 5% of 20 in the 2010s.
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 gross alpha (12% of 17 samples), radium (226 + 228) (10% of 20 samples), and arsenic (6% of 53 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 Dimmit County
- 1Gross alpha12% of 17 local samples were above the limit.
- 2Radium (226 + 228)10% of 20 local samples were above the limit.
- 3Arsenic6% of 53 local samples were above the limit.
- 4Nitrate4% of 54 local samples were above the limit.
- 5Fluoride3% of 120 local samples were above the limit.
- 6Coliform bacteriaRecommended for every private well, every year.
- 7RadonMedian local reading is 150 pCi/L.
- 8Volatile organic compounds (VOCs)22 leaking underground storage tank sites on record locally.
Test your Dimmit County well for gross alpha, radium (226 + 228) and arsenic
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 Dimmit County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Dimmit County
Texas coastal uplands aquifer system
Semiconsolidated sand. Coastal plain sands like these give steady yields at moderate depth. Salt water and sodium are the usual issues near the coast, and nitrate where the water table is shallow; arsenic and radon from bedrock are less common.
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 Dimmit County
TCEQ records 22 leaking underground storage tank sites in Dimmit County, among 28 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.
- 22
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 6
- lined landfills and transfer facilities
Treatment that fits the local profile
Gross alpha
Point-of-use reverse osmosis; Water softener (cation exchange) for radium; Anion exchange for uranium
Radium (226 + 228)
Water softener (cation exchange); Point-of-use reverse osmosis
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Fluoride
Point-of-use reverse osmosis; Activated alumina; 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 gross alpha
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
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.
Free, no obligation
Get on the list for a free in-home water test in Dimmit County
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Common questions
Is there arsenic in well water in Dimmit County?
Arsenic was detected in 30% of 53 public well samples in Dimmit County, and 6% 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 often should I test a private well in Dimmit 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 Dimmit 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
- Texas Water Development Board Groundwater Database: 634 samples in Dimmit 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 Water Quality Portal: 130 samples in Dimmit 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 1,408 people on private wells in Dimmit 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: 28 regulated sites located in Dimmit 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.