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Water wells in the Lower Trinity, Hays County, Texas

Home water wells that draw from the Lower Trinity in Hays County, Texas are typically 464 to 725 feet deep (median 530 ft, 357 wells drilled in the last 10 years). It accounts for 41% of the 862 county wells the state's model covers; the main layer is the Middle Trinity (57%). They are about as deep as the county's median well (510 ft). Estimated cost of a complete well at the median depth: $16,000 to $38,500.

Updated every day from Texas Water Development Board driller reports. Last update: November 11, 2026, using the state file of November 10, 2026.

All wells in Hays CountyLower Trinity across Texas

Which layer Hays County wells draw from

  • Middle Trinity 57% · 495 wells
  • Lower Trinity 41% · 357 wells
  • Near or below the base of the Trinity 1% · 8 wells
  • Upper Trinity <1% · 2 wells

Under Dripping Springs, Hays County

County home wells covered by the Hill Country Trinity model (in the last 10 years).

Home wells in Hays County

Each dot is a home well from a state driller report, colored by depth. Tap one for its details and official report. Tap an empty spot to see what is under that point.

See underground

Well depth (ft)

  • <100
  • 100
  • 200
  • 300
  • 400
  • 600
  • 800+

Dark line: Hays County

Key figures

Typical depth (middle half)
464 to 725 feet
Median depth
530 feet
Deepest 10% are past
830 feet
Water level (median)
343 feet
279 wells
Yield (median)
25 gpm
333 wells, gallons per minute
Wells used
357
In the last 10 years
Share of the county's wells
41%
All years on file
1,205
median 548 ft, since 2000
Confidence
Standard (30 or more wells)

When the wells were finished, the water stood a median 343 feet below the surface (279 wells).

Which layer Hays County wells draw from

  • Middle Trinity 57% · 495 wells
  • Lower Trinity 41% · 357 wells
  • Near or below the base of the Trinity 1% · 8 wells
  • Upper Trinity <1% · 2 wells
County home wells covered by the Hill Country Trinity model (in the last 10 years).

What this layer is

The Lower Trinity groups the Sycamore Sand, the Sligo Formation and the Hosston Formation, under the Hammett Shale. It is the deepest of the four layers in the state's Hill Country model, so wells that draw from it are the deepest and cost the most to drill.

Checked against the state's own aquifer codes: where our method names this layer, the state agrees in 53% of 426 wells. Read it as the likely layer, not a certain one.

More about the Lower Trinity

Depth over time

Home well depth in this layer in Hays County has not changed meaningfully in 20 years: the median was 582 feet in 2003 to 2007 and 530 feet in 2021 to 2025 (a difference under 10% or within the margin of error).

PeriodMedian depth (ft)Wells
2001–2005589240
2006–2010575320
2011–2015500256
2016–2020530178
2021–2025530186
202656019

Places in Hays County with wells in this layer

Common questions

How deep is a well in the Lower Trinity in Hays County?

Home water wells that draw from the Lower Trinity in Hays County, Texas are typically 464 to 725 feet deep (median 530 ft, 357 wells drilled in the last 10 years).

How many Hays County wells draw from this layer?

It accounts for 41% of the 862 county wells the state's model covers; the main layer is the Middle Trinity (57%). For 95% of these wells the report says where the water enters (the screen or the open hole), and we use the middle of that interval.

How deep does the water stand?

When the wells were finished, the water stood a median 343 feet below the surface (279 wells).

What a well costs here

At the median depth for this layer in Hays County (530 feet), a complete home well would cost roughly $16,000 to $38,500: $25 to $60 per foot for drilling, casing and seal, plus $2,500 to $6,500 for the pump, pressure tank, controls and hookup at the well. Across the whole middle half of depths (464 to 725 feet) the range runs from $14,000 to $50,000. This is TerraFunded's estimate from published Texas prices, not a quote, and it leaves out trenching and the line to the house. Get prices from at least two licensed drillers.

How these numbers are made

We count new and replacement domestic (home) wells with a valid depth on their report. We use the last 10 years when there are at least 30 wells; otherwise all since 2001. The median is the middle well and the middle half runs from the 25th to the 75th percentile.

To tell which layer a well draws from, we take the ground elevation at its location, subtract the depth of the interval where water enters (or the bottom of the hole when the report does not give one) and see which layer of the state's model that point falls in.

For 95% of these wells the report says where the water enters (the screen or the open hole), and we use the middle of that interval.

How well it works: In 2,665 wells in the Texas Hill Country where the State of Texas recorded the aquifer, our estimate of the formation the well draws from names the same layer of the state's model in about 76% of them, and that layer or the one next to it in at least 98%.

  • The layers come from the Texas Water Development Board's Hill Country Trinity model, with 1 mile cells. It is a regional model, not a survey of any lot: between one model point and the next, the real depth of each layer can differ.
  • "Near or below the base of the Trinity" means the well reaches the bottom of the model or passes it, often by tens of feet. Older rock that the model does not include may lie there.
  • We never use the model's water levels. The water level on this page is the one each driller measured when the well was finished.

These are depths of real wells drilled nearby, not a promise about any property. Groundwater can change over short distances and with drought. A licensed water well driller can tell you what to expect on a specific tract.

Read the full methodology · Download the data (CSV, CC BY 4.0)

How to cite

TerraFunded (2026). Texas Well Atlas: Underground. From Texas Water Development Board driller reports and groundwater availability models (data as of November 10, 2026). https://terrafunded.com/wells/hays-county/lower-trinity. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources