Well water in Bexar County, Texas
In Bexar County, 11% of 70 tested well samples exceeded the EPA limit for E. coli (0 MPN/100mL), based on public data from USGS Water Quality Portal and Texas Water Development Board Groundwater Database.
412 individual samples from 120 wells, 1953 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 Bexar 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 | |
|---|---|---|---|---|---|---|---|
| E. coli 2004 to 2018 | 70 | 11% | 11% | 0 | 130 | 0 MPN/100mL EPA limit | |
| Fluoride 1959 to 2026 | 119 | 99% | 3% | 0.2 | 4.2 | 4 mg/L EPA limit | |
| Lead 1969 to 2026 | 73 | 44% | 1% | 0 | 20 | 15 ug/L EPA limit | |
| Uranium 1996 to 2026 | 412 | 82% | 0% | 0.732 | 4.2 | 30 ug/L EPA limit | |
| Arsenic 1969 to 2026 | 101 | 48% | 0% | 0 | 2 | 10 ug/L EPA limit | |
| Radium (226 + 228) 1994 to 2018 | 98 | 70% | 0% | 0.17 | 3.7 | 5 pCi/L EPA limit | |
| Copper 1968 to 2026 | 76 | 75% | 0% | 0.002 | 0.04 | 1.3 mg/L EPA limit | |
| Nitrate 1970 to 2026 | 62 | 85% | 0% | 1.3 | 9.85 | 10 mg/L EPA limit | |
| Chloride 1962 to 2026 | 187 | 100% | no limit | 16 | 1,100 | 250 mg/L nuisance level | |
| Sodium 1968 to 2026 | 119 | 100% | no limit | 8 | 510 | 20 mg/L health guideline | |
| Iron 1953 to 2026 | 69 | 59% | no limit | 10 | 6,200 | 300 ug/L nuisance level | |
| Manganese 1956 to 2026 | 62 | 37% | no limit | 0 | 825 | 300 ug/L health guideline | |
| Radon 1990 to 2017 | 40 | 83% | no limit | 78.5 | 570 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOA (7), PFOS (7), Gross alpha (3).
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What this means
The contaminants most often above their limit here are e. coli (11% of 70 samples), fluoride (3% of 119 samples), and lead (1% of 73 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 Bexar County
- Volatile organic compounds (VOCs)1,792 leaking underground storage tank sites on record locally.
- Metals panel10 hazardous waste sites on record locally.
- E. coli11% of 70 local samples were above the limit.
- Fluoride3% of 119 local samples were above the limit.
- Lead1% of 73 local samples were above the limit.
- RadonMedian local reading is 78.5 pCi/L.
- ChlorideDetected in 100% of local samples.
- NitrateRecommended for every private well, especially near farms or septic systems.
- CopperDetected in 75% of local samples.
Contamination sources on record in Bexar County
TCEQ records 1,792 leaking underground storage tank sites and 10 hazardous waste sites in Bexar County, among 1,872 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.
- 1,792
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 10
- hazardous waste sitesSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 70
- lined landfills and transfer facilities
Treatment that fits the local profile
- E. coli
- Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Lead
- Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching
- Copper
- Neutralizing filter to raise pH; Point-of-use reverse osmosis
- Chloride
- Point-of-use reverse osmosis; Distillation
Get your Bexar 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 Bexar County.
Common questions
Is there arsenic in well water in Bexar County?
Arsenic was detected in 48% of 101 public well samples in Bexar 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 Bexar County?
The median radon level across 40 public samples in Bexar County was 78.5 pCi/L, with a high of 570 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Bexar 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
- USGS Water Quality Portal: 835 samples in Bexar 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.
- Texas Water Development Board Groundwater Database: 670 samples in Bexar 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: 1,872 regulated sites located in Bexar 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.