Well water in Starr County, Texas
In Starr County, 53% of 34 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from Texas Water Development Board Groundwater Database.
87 individual samples from 64 wells, 1945 to 2025. Data refreshed September 9, 2026.
TWDB samples an ambient monitoring network of wells on a rotation, so these describe aquifers, not a survey of homeowners' 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 | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| Nitrate 1992 to 2025 | 34 | 97% | 53% | 10.3 | 79.4 | 10 mg/L EPA limit | |
| Arsenic 1992 to 2025 | 34 | 79% | 47% | 6.95 | 99.4 | 10 ug/L EPA limit | |
| Gross alpha 1992 to 2025 | 16 | 63% | 13% | 6.31 | 55 | 15 pCi/L EPA limit | |
| Uranium 2009 to 2025 | 11 | 100% | 9% | 15.8 | 30.2 | 30 ug/L EPA limit | |
| Fluoride 1976 to 2025 | 41 | 90% | 2% | 0.718 | 4.3 | 4 mg/L EPA limit | |
| Lead 1992 to 2025 | 34 | 3% | 0% | 0 | 2.04 | 15 ug/L EPA limit | |
| Copper 1992 to 2025 | 34 | 76% | 0% | 0.004 | 0.035 | 1.3 mg/L EPA limit | |
| Radium (226 + 228) 2009 to 2013 | 10 | 90% | 0% | 0.055 | 0.44 | 5 pCi/L EPA limit | |
| Chloride 1945 to 2025 | 87 | 100% | no limit | 873 | 15,800 | 250 mg/L nuisance level | |
| Sodium 1945 to 2025 | 85 | 100% | no limit | 604 | 9,290 | 20 mg/L health guideline | |
| Iron 1992 to 2025 | 34 | 29% | no limit | 0 | 694 | 300 ug/L nuisance level | |
| Manganese 1992 to 2025 | 34 | 44% | no limit | 0 | 63.9 | 300 ug/L health guideline |
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What 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
- Volatile organic compounds (VOCs)31 leaking underground storage tank sites on record locally.
- Nitrate53% of 34 local samples were above the limit.
- Arsenic47% of 34 local samples were above the limit.
- Gross alpha13% of 16 local samples were above the limit.
- Uranium9% of 11 local samples were above the limit.
- Fluoride2% of 41 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- ChlorideDetected in 100% of local samples.
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
Get your Starr County water tested at home
A licensed local water treatment company tests your tap water in your home, walks you through the numbers, and quotes treatment only if something needs fixing. Free, about 30 minutes, no obligation. Tell us what you need and we match you with a company that serves Starr County.
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.
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.
- 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.