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Water wells in the Lower Trinity, Bexar County, Texas

Home water wells that draw from the Lower Trinity in Bexar County, Texas are typically 500 to 871 feet deep (median 600 ft, 240 wells reported since 2001). It is a minor layer here: just 6% of the 394 wells the state's model covers; the main one is the Middle Trinity (89%). They run about 100 feet deeper than the county's median well (500 ft). Estimated cost of a complete well at the median depth: $17,500 to $42,500.

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 Bexar CountyLower Trinity across Texas

Which layer Bexar County wells draw from

Under San Antonio, Bexar County

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

Home wells in Bexar 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: Bexar County

Key figures

Typical depth (middle half)
500 to 871 feet
Median depth
600 feet
Deepest 10% are past
980 feet
Water level (median)
330 feet
195 wells
Yield (median)
20 gpm
204 wells, gallons per minute
Wells used
240
Since 2001
Share of the county's wells
6%
All years on file
240
median 600 ft, since 2002
Confidence
Standard (30 or more wells)

When the wells were finished, the water stood a median 330 feet below the surface (195 wells).

Which layer Bexar County wells draw from

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

There are not enough wells in both 2003 to 2007 and 2021 to 2025 (at least 30 in each) to say with confidence whether wells in this layer in Bexar County are getting deeper. For reference, the median was 510 feet in 2001 to 2005 (41 wells) and 680 feet in 2021 to 2025 (13 wells).

PeriodMedian depth (ft)Wells
2001–200551041
2006–2010585103
2011–201570067
2016–202056313
2021–202568013
2026under 10 wells3

Places in Bexar County with wells in this layer

Common questions

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

Home water wells that draw from the Lower Trinity in Bexar County, Texas are typically 500 to 871 feet deep (median 600 ft, 240 wells reported since 2001).

How many Bexar County wells draw from this layer?

It is a minor layer here: just 6% of the 394 wells the state's model covers; the main one is the Middle Trinity (89%). Only 11% 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 330 feet below the surface (195 wells).

What a well costs here

At the median depth for this layer in Bexar County (600 feet), a complete home well would cost roughly $17,500 to $42,500: $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 (500 to 871 feet) the range runs from $15,000 to $59,000. 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.

Only 11% 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/bexar-county/lower-trinity. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources