Well water in Hays County, Texas
In Hays County, 6% of 332 tested well samples exceeded the EPA limit for fluoride (4 mg/L), based on public data from Texas Water Development Board Groundwater Database and USGS Water Quality Portal.
354 individual samples from 234 wells, 1937 to 2025. 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 Hays 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 | |
|---|---|---|---|---|---|---|---|
| Fluoride 1952 to 2025 | 332 | 98% | 6% | 0.86 | 8 | 4 mg/L EPA limit | |
| Nitrate 1954 to 2025 | 222 | 64% | <1% | 0.319 | 12.2 | 10 mg/L EPA limit | |
| Uranium 1980 to 2025 | 230 | 57% | 0% | 0.528 | 5.13 | 30 ug/L EPA limit | |
| Arsenic 1976 to 2025 | 175 | 14% | 0% | 0 | 6.3 | 10 ug/L EPA limit | |
| Copper 1988 to 2025 | 167 | 59% | 0% | 0.002 | 0.059 | 1.3 mg/L EPA limit | |
| Lead 1968 to 2025 | 163 | 7% | 0% | 0 | 4 | 15 ug/L EPA limit | |
| Radium (226 + 228) 1980 to 2023 | 27 | 70% | 0% | 0.27 | 1.3 | 5 pCi/L EPA limit | |
| E. coli 2008 to 2018 | 25 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Gross alpha 1988 to 2023 | 12 | 25% | 0% | 0 | 11 | 15 pCi/L EPA limit | |
| Total coliform 2012 to 2017 | 11 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Chloride 1937 to 2025 | 354 | 99% | no limit | 15 | 3,900 | 250 mg/L nuisance level | |
| Sodium 1937 to 2025 | 330 | 100% | no limit | 11 | 2,000 | 20 mg/L health guideline | |
| Iron 1942 to 2025 | 225 | 36% | no limit | 0 | 4,100 | 300 ug/L nuisance level | |
| Manganese 1983 to 2025 | 197 | 40% | no limit | 0 | 145 | 300 ug/L health guideline | |
| Radon 1996 to 2017 | 12 | 100% | no limit | 141 | 460 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOA (2), PFOS (2).
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What this means
The contaminants most often above their limit here are fluoride (6% of 332 samples) and nitrate (<1% of 222 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 Hays County
- Volatile organic compounds (VOCs)124 leaking underground storage tank sites on record locally.
- Metals panel1 hazardous waste site on record locally.
- Fluoride6% of 332 local samples were above the limit.
- Nitrate<1% of 222 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 141 pCi/L.
- ChlorideDetected in 99% of local samples.
- CopperDetected in 59% of local samples.
Contamination sources on record in Hays County
TCEQ records 124 leaking underground storage tank sites and 1 hazardous waste site in Hays County, among 137 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.
- 124
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 1
- hazardous waste siteSolvents, degreasers and metals from industrial sites can travel far in fractured bedrock.
- 12
- lined landfills and transfer facilities
Treatment that fits the local profile
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
- Copper
- Neutralizing filter to raise pH; Point-of-use reverse osmosis
- Chloride
- Point-of-use reverse osmosis; Distillation
Get your Hays 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 Hays County.
Common questions
Is there arsenic in well water in Hays County?
Arsenic was detected in 14% of 175 public well samples in Hays 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 Hays County?
The median radon level across 12 public samples in Hays County was 141 pCi/L, with a high of 460 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Hays 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: 2,238 samples in Hays 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: 248 samples in Hays 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: 137 regulated sites located in Hays 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.