Well water in Starr County, Texas
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Testing strongly recommended
tested well samples in Starr County exceeded the EPA limit for nitrate (10 mg/L), based on public data from Texas Water Development Board Groundwater Database.
454 test results across 12 contaminants from at least 64 wells, 1945 to 2025; chloride has the most at 87. 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 3,296 people in Starr County get their drinking water from a private well, per USGS 2015 county water use. That is about 5% of residents.
Separately, the USGS national arsenic model estimates that 75% of the 3,296 people on private wells in Starr County draw water above 10 ug/L (the model's range is 56% to 96%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Starr 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 1992 to 2025 | 34 | 97% | 10.3 | 79.4 | 10 mg/L EPA limit | |
| Arsenic 1992 to 2025 | 34 | 79% | 6.95 | 99.4 | 10 ug/L EPA limit | |
| Gross alpha 1992 to 2025 | 16 | 63% | 6.31 | 55 | 15 pCi/L EPA limit | |
| Uranium 2009 to 2025 | 11 | 100% | 15.8 | 30.2 | 30 ug/L EPA limit | |
| Fluoride 1976 to 2025 | 41 | 90% | 0.718 | 4.3 | 4 mg/L EPA limit | |
| Copper 1992 to 2025 | 34 | 76% | 0.004 | 0.035 | 1.3 mg/L EPA limit | |
| Lead 1992 to 2025 | 34 | 3% | 0 | 2.04 | 15 ug/L EPA limit | |
| Radium (226 + 228) 2009 to 2013 | 10 | 90% | 0.055 | 0.44 | 5 pCi/L EPA limit | |
| Chloride 1945 to 2025 | no limit | 87 | 100% | 873 | 15,800 | 250 mg/L nuisance level |
| Sodium 1945 to 2025 | no limit | 85 | 100% | 604 | 9,290 | 20 mg/L health guideline |
| Iron 1992 to 2025 | no limit | 34 | 29% | 0 | 694 | 300 ug/L nuisance level |
| Manganese 1992 to 2025 | no limit | 34 | 44% | 0 | 63.9 | 300 ug/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 |
|---|---|---|---|---|
| Fluoride | 5%22 samples | 0%11 samples | n/a | n/a |
| Nitrate | 40%15 samples | 64%11 samples | n/a | n/a |
| Arsenic | 33%15 samples | 73%11 samples | n/a | n/a |
| Copper | 0%15 samples | 0%11 samples | n/a | n/a |
| Lead | 0%15 samples | 0%11 samples | n/a | n/a |
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 (53% of 34 samples), arsenic (47% of 34 samples), and gross alpha (13% of 16 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 Starr County
- 1Nitrate53% of 34 local samples were above the limit.
- 2Arsenic47% of 34 local samples were above the limit.
- 3Gross alpha13% of 16 local samples were above the limit.
- 4Uranium9% of 11 local samples were above the limit.
- 5Fluoride2% of 41 local samples were above the limit.
- 6Coliform bacteriaRecommended for every private well, every year.
- 7ChlorideDetected in 100% of local samples.
- 8Volatile organic compounds (VOCs)31 leaking underground storage tank sites on record locally.
Test your Starr County well for nitrate, arsenic and gross alpha
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 Starr County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Starr County
Coastal lowlands 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 Starr County
TCEQ records 31 leaking underground storage tank sites in Starr County, among 37 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.
- 31
- 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
Nitrate
Point-of-use reverse osmosis; Anion exchange; Distillation
Arsenic
Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
Gross alpha
Point-of-use reverse osmosis; Water softener (cation exchange) for radium; Anion exchange for uranium
Uranium
Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
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 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.
Free, no obligation
Get on the list for a free in-home water test in Starr County
No water treatment company serves Starr 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 Starr County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Starr County?
Arsenic was detected in 79% of 34 public well samples in Starr County, and 47% 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 Starr 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 Starr 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: 454 samples in Starr 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 3,296 people on private wells in Starr 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: 37 regulated sites located in Starr 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.