Well water in Gillespie County, Texas
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Testing recommended
tested well samples in Gillespie County exceeded the EPA limit for gross alpha (15 pCi/L), based on public data from Texas Water Development Board Groundwater Database and USGS Water Quality Portal.
1,131 test results across 12 contaminants from at least 128 wells, 1936 to 2024; chloride has the most at 225. 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 10,267 people in Gillespie County get their drinking water from a private well, per USGS 2015 county water use. That is about 40% of residents.
Separately, the USGS national arsenic model estimates that 1% of the 10,267 people on private wells in Gillespie County draw water above 10 ug/L (the model's range is <1% to 2%), from geology and well depth rather than local tests.
What individual samples found
Each row summarizes every public sample for that contaminant inside Gillespie 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 |
|---|---|---|---|---|---|---|
| Gross alpha 1989 to 2024 | 31 | 61% | 4.27 | 18 | 15 pCi/L EPA limit | |
| Nitrate 1989 to 2024 | 68 | 93% | 1.73 | 17.6 | 10 mg/L EPA limit | |
| Radium (226 + 228) 1990 to 2020 | 44 | 91% | 1.56 | 6.8 | 5 pCi/L EPA limit | |
| Fluoride 1954 to 2024 | 219 | 95% | 0.4 | 2.23 | 4 mg/L EPA limit | |
| Arsenic 1989 to 2024 | 59 | 12% | 0 | 2.7 | 10 ug/L EPA limit | |
| Lead 1990 to 2024 | 56 | 7% | 0 | 4.69 | 15 ug/L EPA limit | |
| Copper 1990 to 2024 | 56 | 79% | 0.004 | 0.026 | 1.3 mg/L EPA limit | |
| Uranium 2008 to 2024 | 20 | 80% | 1.66 | 3.1 | 30 ug/L EPA limit | |
| Chloride 1936 to 2024 | no limit | 225 | 100% | 34 | 653 | 250 mg/L nuisance level |
| Sodium 1936 to 2024 | no limit | 218 | 99% | 26 | 764 | 20 mg/L health guideline |
| Iron 1954 to 2024 | no limit | 75 | 41% | 0 | 21,000 | 300 ug/L nuisance level |
| Manganese 1954 to 2024 | no limit | 60 | 37% | 0 | 40 | 300 ug/L health guideline |
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 |
|---|---|---|---|---|
| Fluoride | 0%175 samples | 0%28 samples | 0%11 samples | n/a |
| Nitrate | 5%21 samples | 10%31 samples | 0%11 samples | n/a |
| Arsenic | 0%21 samples | 0%27 samples | n/a | n/a |
| Lead | 0%18 samples | 0%27 samples | n/a | n/a |
| Copper | 0%18 samples | 0%27 samples | n/a | n/a |
| Radium (226 + 228) | 10%10 samples | 0%18 samples | 8%12 samples | n/a |
Nitrate above the limit in Gillespie County rose from 5% of 21 samples before 2000 to 10% of 31 in the 2000s.
Fluoride, arsenic 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 addressWhat this means
The contaminants most often above their limit here are gross alpha (6% of 31 samples), nitrate (6% of 68 samples), and radium (226 + 228) (5% of 44 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 Gillespie County
- 1Gross alpha6% of 31 local samples were above the limit.
- 2Nitrate6% of 68 local samples were above the limit.
- 3Radium (226 + 228)5% of 44 local samples were above the limit.
- 4Coliform bacteriaRecommended for every private well, every year.
- 5ChlorideDetected in 100% of local samples.
- 6FluorideDetected in 95% of local samples.
- 7CopperDetected in 79% of local samples.
- 8Volatile organic compounds (VOCs)45 leaking underground storage tank sites on record locally.
Test your Gillespie County well for gross alpha, nitrate and radium (226 + 228)
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 $209Already 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 Gillespie County numbers, $29. Every line explained, ranked by what matters, with the fix for each.
The rock under Gillespie County
Edwards-Trinity aquifer system
Sandstone and carbonate-rock. Layered sandstone and limestone means a well may draw from either. Hardness and iron are routine, and the limestone layers can carry bacteria and nitrate from the surface quickly, so test for both yearly.
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 Gillespie County
TCEQ records 45 leaking underground storage tank sites in Gillespie County, among 48 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.
- 45
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 3
- 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
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 gross alpha
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.
Free, no obligation
Get on the list for a free in-home water test in Gillespie County
No water treatment company serves Gillespie 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 Gillespie County, and you get an email naming it first.
Common questions
Is there arsenic in well water in Gillespie County?
Arsenic was detected in 12% of 59 public well samples in Gillespie 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 often should I test a private well in Gillespie 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 Gillespie 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
- Texas Water Development Board Groundwater Database: 1,127 samples in Gillespie 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: 4 samples in Gillespie 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.
- USGS national arsenic model (Ayotte 2017): estimated share of 10,267 people on private wells in Gillespie 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: 48 regulated sites located in Gillespie 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.