Well water in Williamson County, Texas
In Williamson County, 25% of 296 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.
315 individual samples from 185 wells, 1940 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 Williamson 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 1940 to 2023 | 296 | 99% | 25% | 2.9 | 7.6 | 4 mg/L EPA limit | |
| Nitrate 1972 to 2023 | 32 | 44% | 3% | 0 | 12.4 | 10 mg/L EPA limit | |
| Uranium 2007 to 2023 | 46 | 63% | 0% | 0.296 | 1.6 | 30 ug/L EPA limit | |
| Copper 1989 to 2023 | 29 | 45% | 0% | 0 | 0.22 | 1.3 mg/L EPA limit | |
| Arsenic 1993 to 2023 | 28 | 18% | 0% | 0 | 2.87 | 10 ug/L EPA limit | |
| Lead 1993 to 2023 | 28 | 0% | 0% | 0 | 0 | 15 ug/L EPA limit | |
| Radium (226 + 228) 2011 to 2018 | 16 | 69% | 0% | 0.855 | 4.2 | 5 pCi/L EPA limit | |
| Gross alpha 1993 to 2023 | 11 | 55% | 0% | 1.5 | 10.7 | 15 pCi/L EPA limit | |
| Chloride 1940 to 2023 | 315 | 100% | no limit | 44 | 1,640 | 250 mg/L nuisance level | |
| Sodium 1940 to 2023 | 309 | 100% | no limit | 69.5 | 1,740 | 20 mg/L health guideline | |
| Iron 1967 to 2023 | 38 | 45% | no limit | 0 | 2,040 | 300 ug/L nuisance level | |
| Manganese 1980 to 2023 | 32 | 38% | no limit | 0 | 37 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: PFOA (2), PFOS (2), E. coli (3), Radon (3).
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What this means
The contaminants most often above their limit here are fluoride (25% of 296 samples) and nitrate (3% of 32 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 Williamson County
- Volatile organic compounds (VOCs)187 leaking underground storage tank sites on record locally.
- Fluoride25% of 296 local samples were above the limit.
- Nitrate3% of 32 local samples were above the limit.
- RadonMedian local reading is 320 pCi/L.
- PFOAAbove the limit in 1 of 2 local samples; too few to quote a rate.
- PFOSAbove the limit in 1 of 2 local samples; too few to quote a rate.
- E. coliAbove the limit in 1 of 3 local samples; too few to quote a rate.
- ChlorideDetected in 100% of local samples.
Contamination sources on record in Williamson County
TCEQ records 187 leaking underground storage tank sites in Williamson County, among 200 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.
- 187
- leaking underground storage tank sitesGasoline and heating oil that leaked from tanks move through groundwater as benzene, MTBE and other volatile organic compounds.
- 13
- 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
- Chloride
- Point-of-use reverse osmosis; Distillation
Get your Williamson 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 Williamson County.
Common questions
Is there arsenic in well water in Williamson County?
Arsenic was detected in 18% of 28 public well samples in Williamson 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 Williamson County?
The median radon level across 3 public samples in Williamson County was 320 pCi/L, with a high of 410 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Williamson 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: 1,140 samples in Williamson 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: 50 samples in Williamson 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: 200 regulated sites located in Williamson 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.