Well water in Presidio County, Texas
In Presidio County, 31% of 48 tested well samples 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.
64 individual samples from 40 wells, 1942 to 2023. 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 Presidio 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 1980 to 2023 | 48 | 77% | 31% | 5.88 | 44.3 | 10 ug/L EPA limit | |
| Fluoride 1955 to 2023 | 61 | 98% | 23% | 2.02 | 9.55 | 4 mg/L EPA limit | |
| Gross alpha 1990 to 1994 | 16 | 94% | 13% | 5.85 | 27 | 15 pCi/L EPA limit | |
| Nitrate 1991 to 2023 | 43 | 88% | 2% | 1.14 | 10.6 | 10 mg/L EPA limit | |
| Lead 1990 to 2023 | 47 | 0% | 0% | 0 | 0 | 15 ug/L EPA limit | |
| Copper 1990 to 2023 | 46 | 43% | 0% | 0 | 0.012 | 1.3 mg/L EPA limit | |
| Radium (226 + 228) 1990 to 2014 | 12 | 33% | 0% | 0 | 1.9 | 5 pCi/L EPA limit | |
| Chloride 1942 to 2023 | 64 | 98% | no limit | 21.3 | 520 | 250 mg/L nuisance level | |
| Sodium 1955 to 2023 | 62 | 100% | no limit | 81.9 | 601 | 20 mg/L health guideline | |
| Iron 1971 to 2023 | 52 | 31% | no limit | 0 | 992 | 300 ug/L nuisance level | |
| Manganese 1971 to 2023 | 50 | 44% | no limit | 0 | 190 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Uranium (6), E. coli (1), Radon (1).
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What this means
The contaminants most often above their limit here are arsenic (31% of 48 samples), fluoride (23% of 61 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 Presidio County
- Volatile organic compounds (VOCs)15 leaking underground storage tank sites on record locally.
- Arsenic31% of 48 local samples were above the limit.
- Fluoride23% of 61 local samples were above the limit.
- Gross alpha13% of 16 local samples were above the limit.
- Nitrate2% of 43 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 590 pCi/L.
- ChlorideDetected in 98% of local samples.
Contamination sources on record in Presidio County
TCEQ records 15 leaking underground storage tank sites in Presidio County, among 20 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.
- 15
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 5
- 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
- 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
- Chloride
- Point-of-use reverse osmosis; Distillation
Get your Presidio 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 Presidio County.
Common questions
Is there arsenic in well water in Presidio County?
Arsenic was detected in 77% of 48 public well samples in Presidio County, and 31% 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 Presidio County?
The median radon level across 1 public samples in Presidio County was 590 pCi/L, with a high of 590 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Presidio 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: 502 samples in Presidio 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: 7 samples in Presidio 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: 20 regulated sites located in Presidio 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.