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Water wells in the Lower Trinity, Gillespie County, Texas

Only 11 home water wells that draw from the Lower Trinity in Gillespie County, Texas have been reported since 2001, so treat this as a rough guide: the middle half are 605 to 650 feet deep (median 650 ft). It is a minor layer here: just under 1% of the 1,335 wells the state's model covers; the main one is the Middle Trinity (51%). They run about 410 feet deeper than the county's median well (240 ft). Estimated cost of a complete well at the median depth: $19,000 to $45,500.

This page is based on fewer than 30 wells, so it is kept out of search engines until more reports come in. Treat every figure as a rough guide.

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 Gillespie CountyLower Trinity across Texas

Which layer Gillespie County wells draw from

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

Home wells in Gillespie 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: Gillespie County

Key figures

Typical depth (middle half)
605 to 650 feet
Median depth
650 feet
Deepest 10% are past
650 feet
Water level (median)
381 feet
10 wells
Wells used
11
Since 2001
Share of the county's wells
<1%
All years on file
11
median 650 ft, since 2003
Confidence
Few wells (10 to 29)

When the wells were finished, the water stood a median 381 feet below the surface (10 wells).

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

Too few wells per period in this layer in Gillespie County to compare depth over time. Since 2003, 11 home wells have been reported, with a median of 650 feet.

PeriodMedian depth (ft)Wells
2001–2005under 10 wells2
2006–2010under 10 wells3
2021–2025under 10 wells3
2026under 10 wells3

Common questions

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

Only 11 home water wells that draw from the Lower Trinity in Gillespie County, Texas have been reported since 2001, so treat this as a rough guide: the middle half are 605 to 650 feet deep (median 650 ft).

How many Gillespie County wells draw from this layer?

It is a minor layer here: just under 1% of the 1,335 wells the state's model covers; the main one is the Middle Trinity (51%). Only 46% of these wells have the water-bearing interval on their report (reports before about 2012 rarely do). For the others we use the bottom of the hole, which tends to read one layer deeper than where the water actually comes from.

How deep does the water stand?

When the wells were finished, the water stood a median 381 feet below the surface (10 wells).

What a well costs here

At the median depth for this layer in Gillespie County (650 feet), a complete home well would cost roughly $19,000 to $45,500: $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 (605 to 650 feet) the range runs from $17,500 to $45,500. 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.

Only 46% of these wells have the water-bearing interval on their report (reports before about 2012 rarely do). For the others we use the bottom of the hole, which tends to read one layer deeper than where the water actually comes from.

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/gillespie-county/lower-trinity. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources