Well water in Bexar County, Texas

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Testing recommended

tested well samples in Bexar County 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.

14,486 test results across 16 contaminants from at least 525 wells, 1908 to 2026; chloride has the most at 3,880. Data refreshed September 15, 2026.

Compiled by Nick at Well Water Nerd from public records. How these pages are built

TWDB samples an ambient monitoring network of wells on a rotation, so these describe aquifers, not a survey of homeowners' tests.

An estimated 73,411 people in Bexar County get their drinking water from a private well, per USGS 2015 county water use. That is about 4% of residents.

Separately, the USGS national arsenic model estimates that <1% of the 73,411 people on private wells in Bexar County draw water above 10 ug/L, from geology and well depth rather than local 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	Above limit	Samples	Detected	Median	Highest	Limit
E. coli 2004 to 2018	11%	70	11%	0	130	0 MPN/100mL EPA limit
Nitrate 1939 to 2026	6%	1,422	95%	1.7	39	10 mg/L EPA limit
Fluoride 1959 to 2026	3%	119	99%	0.2	4.2	4 mg/L EPA limit
Arsenic 1969 to 2026	<1%	1,161	58%	0	77	10 ug/L EPA limit
Lead 1968 to 2026	<1%	1,059	53%	0	37	15 ug/L EPA limit
Copper 1968 to 2026	0%	1,082	69%	0	0.4	1.3 mg/L EPA limit
Uranium 1996 to 2026	0%	412	82%	0.732	4.2	30 ug/L EPA limit
Radium (226 + 228) 1994 to 2018	0%	98	70%	0.17	3.7	5 pCi/L EPA limit
Chloride 1908 to 2026	no limit	3,880	100%	24	4,210	250 mg/L nuisance level
Sodium 1941 to 2026	no limit	2,632	100%	12	1,080	20 mg/L health guideline
Iron 1911 to 2026	no limit	1,301	58%	0	41,000	300 ug/L nuisance level
Manganese 1955 to 2026	no limit	1,193	39%	0	2,900	300 ug/L health guideline
Radon 1990 to 2017	no limit	40	83%	78.5	570	2,000 pCi/L health guideline

Sampled fewer than 10 times, too few to summarize: PFOS (7), PFOA (7), Gross alpha (3).

Over time

Share of samples above the limit by period. A cell needs ten samples to show; a comparison needs twenty in each period. Later periods sample fewer wells, and often the ones already known to have a problem.

Contaminant	before 2000	2000s	2010s	2020s
Nitrate	1%883 samples	12%142 samples	14%282 samples	17%115 samples
Arsenic	<1%769 samples	0%206 samples	0%178 samples	n/a
Copper	0%736 samples	0%208 samples	0%130 samples	n/a
Lead	<1%715 samples	0%208 samples	0%128 samples	n/a
Uranium	0%47 samples	0%171 samples	0%186 samples	n/a
Fluoride	3%102 samples	n/a	0%11 samples	n/a

Nitrate, arsenic, copper, lead, uranium have held within a few points between the two most recent periods with enough samples.

Closer than the county

See the sampled wells near your address

The same records, drawn around one point: which wells within a few miles were sampled and what they found, how deep the wells next to you were drilled, and any leaking tank or cleanup site within a mile.

Check my address

What this means

The contaminants most often above their limit here are e. coli (11% of 70 samples), nitrate (6% of 1,422 samples), and fluoride (3% of 119 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

1
E. coli
11% of 70 local samples were above the limit.
2
Nitrate
6% of 1,422 local samples were above the limit.
3
Fluoride
3% of 119 local samples were above the limit.
4
Arsenic
<1% of 1,161 local samples were above the limit.
5
Lead
<1% of 1,059 local samples were above the limit.
6
Radon
Median local reading is 78.5 pCi/L.
7
Chloride
Detected in 100% of local samples.
8
Volatile organic compounds (VOCs)
1,792 leaking underground storage tank sites on record locally.
9
Metals panel
10 hazardous waste sites on record locally.

Test your Bexar County well for E. coli, nitrate and fluoride

Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.

Order the Tap Score well water test kit, from $209 Already tested? Upload the report

Just want bacteria checked first? Tap Score coliform and E. coli test, $99. Coliform and E. coli are the tests every well needs every year.

Want a quick look before paying for a lab? Home well water test strips on Amazon check hardness, iron, pH and nitrate in minutes. They are a screen, not a result: arsenic, bacteria, uranium and PFAS need a certified lab.

Affiliate links: the merchant pays us a commission and the price is the same for you. It does not change what the data above says. As an Amazon Associate we earn from qualifying purchases.

Where to get a well tested in Texas: certified labs, state programs and prices.

Already have results back? Get your lab report read against the Bexar County numbers, $29. Every line explained, ranked by what matters, with the fix for each.

The rock under Bexar County

Not a principal aquifer

The USGS map places this area outside any principal aquifer, which usually means wells here draw from fractured bedrock or thin local deposits rather than a large regional aquifer. Bedrock wells of that kind are where arsenic, radon and uranium turn up, and yields vary from well to well.

Classification from the USGS Principal Aquifers of the United States (national map, 2003 edition, GIS release 2015), read at the county centroid. A single well can sit in a different unit, especially near a boundary.

Official help in Texas

Two places to start that are not selling anything: the state program that answers private well questions, and its list of labs certified to run drinking water tests. A certified lab is the difference between a result you can act on and a number.

Private Wells, Texas Groundwater Protection Committee
Environmental Laboratory (NELAP) Accreditation, TCEQ

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

Nitrate

Point-of-use reverse osmosis; Anion exchange; Distillation

Fluoride

Point-of-use reverse osmosis; Activated alumina; Distillation

Arsenic

Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange

Lead

Point-of-use reverse osmosis; Certified lead-removal carbon filter; Neutralizing filter to raise pH and stop leaching

Systems we would look at first

Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.

For E. coli

UV disinfection system

whole-house, at the point of entry, about $900

Fix the well cap and casing first; UV keeps bacteria from returning.

For E. coli

Aquasana Rhino Well Water with UV

whole-house, at the point of entry, about $2,871

Whole-house system built for wells: sediment pre-filter, KDF and carbon, and a UV lamp rated to kill 99.99% of bacteria and viruses. It does not remove arsenic, nitrate, uranium or radon.

For nitrate

Under-sink reverse osmosis system

under-sink or countertop, about $300

Look for NSF/ANSI 58 certification listing the contaminant you need removed.

For nitrate

Aquasana SmartFlow reverse osmosis

under-sink or countertop, about $225

Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.

For arsenic

Whole-house arsenic and uranium filter

whole-house, at the point of entry, about $2,500

Adsorptive iron-based media; sized to your well yield.

For lead

Aquasana Claryum 3-Stage under-sink filter

under-sink or countertop, about $175

Certified to NSF/ANSI 53 to reduce 99% of lead and 99.7% of PFOA and PFOS at the tap. Not a fix for arsenic, nitrate or bacteria.

For lead

Acid neutralizing filter

whole-house, at the point of entry, about $1,200

Raises pH so plumbing stops leaching lead and copper.

Free, no obligation

Get on the list for a free in-home water test in Bexar County

No water treatment company serves Bexar County through Well Water Nerd yet. We are signing licensed companies on county by county: they test at your tap for free, walk you through the numbers, and quote treatment only if something needs fixing. Leave your details and you are first in line. Nothing is shared until a company joins for Bexar County, and you get an email naming it first.

Common questions

Is there arsenic in well water in Bexar County?

Arsenic was detected in 58% of 1,161 public well samples in Bexar County, and <1% 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.

Counties near Bexar County

Closest first. Groundwater does not stop at a line on a map, so the next county over is a fair second opinion.

Want the numbers themselves? Download the Texas dataset as CSV, every county and town, with the sources named.

Sources

USGS Water Quality Portal: 13,816 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.
USGS national arsenic model (Ayotte 2017): estimated share of 73,411 people on private wells in Bexar County above 10 ug/L of arsenic, from geology, well depth and land use. County estimates of domestic well users with arsenic above 10 ug/L from the USGS national logistic regression model (Ayotte, Medalie and Qi, 2017), with private well population from the USGS 2015 county water-use compilation (Dieter and others, 2018). Retrieved September 15, 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.