Hays County, Texas: drinking water report. Hays County between Austin and San Antonio has about 247,000 residents in one of the fastest-growing corridors
Hays County between Austin and San Antonio has about 247,000 residents in one of the fastest-growing corridors in Texas. San Marcos and Kyle are the main communities. Water comes from the Edwards Aquifer and the Trinity Aquifer, with Canyon Regional Water Authority and municipal systems serving different areas. The county sits directly over the Edwards Aquifer recharge zone – the area where surface water enters the aquifer.
The Edwards Aquifer recharge zone in Hays County is being paved over at an alarming rate. According to the Edwards Aquifer Authority's 2024 recharge zone monitoring report, impervious cover in the recharge zone has increased by 35% over the past decade as development sprawls along the I-35 corridor. More impervious cover means less recharge and more stormwater contamination reaching the aquifer through the remaining recharge features.
San Marcos Springs – the second-largest spring group in Texas – serves as an indicator for aquifer quality. A 2024 EAA study detected trace PFAS at 3 ppt in spring water, likely from diffuse urban sources. The Trinity Aquifer in the western part of the county shows naturally elevated fluoride, with some wells approaching the 4 mg/L MCL.
Hays County's position over the Edwards recharge zone means every parking lot, gas station, and septic system built here affects aquifer quality. The aquifer is resilient but not invulnerable, and the pace of development is testing its limits.
Check your water for data at your address. For fluoride from the Trinity Aquifer and emerging PFAS, reverse osmosis handles both. Our water filter guide covers systems suited to Texas Hill Country water. Pull your detailed report for trends, and visit our Texas page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Hays County, TX.
The EPA places Hays 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.
13% of homes in Hays 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 Hays 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