Well water in McMullen County, Texas
In McMullen County, none of 59 tested well samples exceeded the EPA limit for fluoride, based on public data from Texas Water Development Board Groundwater Database and USGS Water Quality Portal.
72 individual samples from 25 wells, 1950 to 2022. 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 McMullen 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 | |
|---|---|---|---|---|---|---|---|
| Arsenic 1992 to 2022 | 26 | 42% | 38% | 0 | 40 | 10 ug/L EPA limit | |
| Fluoride 1956 to 2022 | 59 | 100% | 0% | 0.6 | 3.9 | 4 mg/L EPA limit | |
| Nitrate 1992 to 2022 | 26 | 58% | 0% | 0.067 | 8.48 | 10 mg/L EPA limit | |
| Lead 1992 to 2022 | 26 | 12% | 0% | 0 | 4.9 | 15 ug/L EPA limit | |
| Copper 1992 to 2022 | 26 | 62% | 0% | 0.002 | 0.069 | 1.3 mg/L EPA limit | |
| Sodium 1956 to 2022 | 72 | 100% | no limit | 307 | 1,820 | 20 mg/L health guideline | |
| Chloride 1956 to 2022 | 72 | 100% | no limit | 125 | 2,500 | 250 mg/L nuisance level | |
| Iron 1950 to 2022 | 43 | 74% | no limit | 116 | 1,320 | 300 ug/L nuisance level | |
| Manganese 1992 to 2022 | 26 | 50% | no limit | 4.43 | 100 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Uranium (8), Gross alpha (8), Radium (226 + 228) (6), E. coli (1), Radon (1).
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What this means
The contaminants most often above their limit here are arsenic (38% of 26 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 and Iron 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 McMullen County
- Volatile organic compounds (VOCs)1 leaking underground storage tank site on record locally.
- Arsenic38% of 26 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 111 pCi/L.
- UraniumAbove the limit in 2 of 8 local samples; too few to quote a rate.
- Gross alphaAbove the limit in 1 of 8 local samples; too few to quote a rate.
- FluorideDetected in 100% of local samples.
- ChlorideDetected in 100% of local samples.
Contamination sources on record in McMullen County
TCEQ records 1 leaking underground storage tank site in McMullen County, among 3 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.
- 1
- leaking underground storage tank siteGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 2
- lined landfills and transfer facilities
Treatment that fits the local profile
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Copper
- Neutralizing filter to raise pH; Point-of-use reverse osmosis
- Chloride
- Point-of-use reverse osmosis; Distillation
- Iron
- Oxidizing filter whole-house; Water softener (low levels); Aeration plus filtration
Get your McMullen 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 McMullen County.
Common questions
Is there arsenic in well water in McMullen County?
Arsenic was detected in 42% of 26 public well samples in McMullen County, and 38% 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 McMullen County?
The median radon level across 1 public samples in McMullen County was 111 pCi/L, with a high of 111 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in McMullen 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: 391 samples in McMullen 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: 9 samples in McMullen 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: 3 regulated sites located in McMullen 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.