Williamson County, Texas: drinking water report. Williamson County sits north of Austin, home to about 650,000 residents in one of the fastest-growing…
Williamson County sits north of Austin, home to about 650,000 residents in one of the fastest-growing counties in Texas. Cities like Round Rock, Cedar Park, and Georgetown draw water from different sources – the Brazos River Authority's Lake Georgetown, Lake Stillhouse Hollow, and the Edwards Aquifer for some western communities. The county's explosive growth has put pressure on both water supply and treatment infrastructure.
Williamson County's water systems have generally maintained good compliance records. The surface water reservoirs draw from relatively clean Hill Country watersheds, though development pressure is increasing runoff into source waters. UCMR5 data shows low-level PFAS detections in some county systems, without the military point sources that affect neighboring counties.
Water hardness is a common concern. The Edwards Limestone aquifer and Hill Country reservoirs produce naturally hard water. According to the City of Round Rock's 2024 water quality report, TDS levels averaged around 380 mg/L – enough to cause noticeable scale buildup but within EPA secondary standards.
Williamson County's rapid growth means new development areas may experience temporary water quality variability. Established systems are generally performing well.
Check your water for data in your area. A water softener addresses hardness; a reverse osmosis system under the sink handles taste, TDS, and PFAS. Our water filter guide covers both. Pull your detailed report, and visit our Texas page for statewide data.
Drinking water is one exposure route. These federal datasets also cover Williamson County, TX.
The EPA places Williamson County, TX in Zone 3 - the EPA's lowest-risk category, with a predicted average indoor radon level below 2 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
11% of homes in Williamson County, TX were built before 1980, and 2% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Williamson County, TX averages 8.5 µg/m³, within the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
25 public water systems serving Williamson County, TX have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 10 water systems serving Williamson County, TX carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Total Trihalomethanes (TTHM) | 4 |
| Total Coliform Rule | 4 |
| Lead and Copper Rule Revisions | 1 |
| Interim Enhanced Surface Water Treatment Rule | 1 |
| Fluoride | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.