Well water in Zavala County, Texas
In Zavala County, 14% of 56 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from Texas Water Development Board Groundwater Database and USGS Water Quality Portal.
82 individual samples from 30 wells, 1928 to 2026. 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 Zavala 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 | |
|---|---|---|---|---|---|---|---|
| Gross alpha 1990 to 2014 | 11 | 73% | 18% | 4.9 | 30 | 15 pCi/L EPA limit | |
| Nitrate 1990 to 2026 | 56 | 57% | 14% | 0.036 | 20.4 | 10 mg/L EPA limit | |
| Radium (226 + 228) 1990 to 2015 | 16 | 81% | 6% | 1.48 | 9.6 | 5 pCi/L EPA limit | |
| Fluoride 1969 to 2026 | 75 | 100% | 0% | 0.3 | 2.1 | 4 mg/L EPA limit | |
| Lead 1990 to 2026 | 56 | 2% | 0% | 0 | 3 | 15 ug/L EPA limit | |
| Arsenic 1990 to 2026 | 56 | 9% | 0% | 0 | 4 | 10 ug/L EPA limit | |
| Copper 1990 to 2026 | 56 | 50% | 0% | 0.001 | 0.017 | 1.3 mg/L EPA limit | |
| Uranium 2008 to 2026 | 35 | 74% | 0% | 1.71 | 11.4 | 30 ug/L EPA limit | |
| Sodium 1928 to 2026 | 82 | 100% | no limit | 75.5 | 790 | 20 mg/L health guideline | |
| Chloride 1928 to 2026 | 82 | 100% | no limit | 58.8 | 1,040 | 250 mg/L nuisance level | |
| Iron 1930 to 2026 | 62 | 53% | no limit | 39.5 | 6,600 | 300 ug/L nuisance level | |
| Manganese 1990 to 2026 | 56 | 75% | no limit | 12.9 | 224 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: E. coli (3), Radon (3).
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What this means
The contaminants most often above their limit here are gross alpha (18% of 11 samples), nitrate (14% of 56 samples), and radium (226 + 228) (6% 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, 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 Zavala County
- Volatile organic compounds (VOCs)20 leaking underground storage tank sites on record locally.
- Metals panel1 hazardous waste site on record locally.
- Gross alpha18% of 11 local samples were above the limit.
- Nitrate14% of 56 local samples were above the limit.
- Radium (226 + 228)6% of 16 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 190 pCi/L.
- FluorideDetected in 100% of local samples.
- ChlorideDetected in 100% of local samples.
Contamination sources on record in Zavala County
TCEQ records 20 leaking underground storage tank sites and 1 hazardous waste site in Zavala County, among 29 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.
- 20
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 1
- hazardous waste siteSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 8
- 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
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
- Radium (226 + 228)
- Water softener (cation exchange); Point-of-use reverse osmosis
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Chloride
- Point-of-use reverse osmosis; Distillation
Get your Zavala 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 Zavala County.
Common questions
Is there arsenic in well water in Zavala County?
Arsenic was detected in 9% of 56 public well samples in Zavala 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 Zavala County?
The median radon level across 3 public samples in Zavala County was 190 pCi/L, with a high of 550 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Zavala 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: 631 samples in Zavala 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: 18 samples in Zavala 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.
- TCEQ regulated sites: 29 regulated sites located in Zavala 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.