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Water wells in the Upper Trinity, Bexar County, Texas

Home water wells that draw from the Upper Trinity in Bexar County, Texas are typically 350 to 650 feet deep (median 450 ft, 57 wells reported since 2001). It is a minor layer here: just 5% of the 394 wells the state's model covers; the main one is the Middle Trinity (89%). They run about 50 feet shallower than the county's median well (500 ft). Estimated cost of a complete well at the median depth: $14,000 to $33,500.

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 CountyUpper 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)
350 to 650 feet
Median depth
450 feet
Deepest 10% are past
800 feet
Water level (median)
235 feet
43 wells
Yield (median)
27.5 gpm
50 wells, gallons per minute
Wells used
57
Since 2001
Share of the county's wells
5%
All years on file
57
median 450 ft, since 1997
Confidence
Standard (30 or more wells)

When the wells were finished, the water stood a median 235 feet below the surface (43 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 Upper Trinity is the upper member of the Glen Rose Limestone: alternating beds of limestone and marl that make the stair-step hills of the Hill Country. It is the first Trinity layer a driller meets and usually the least productive, so many home wells pass through it and are completed deeper.

Checked against the state's own aquifer codes: where our method names this layer, the state agrees in 59% of 347 wells. Read it as the likely layer, not a certain one.

More about the Upper 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 420 feet in 2001 to 2005 (17 wells) and 440 feet in 2021 to 2025 (14 wells).

PeriodMedian depth (ft)Wells
2001–200542017
2006–201060011
2011–2015under 10 wells7
2016–2020under 10 wells6
2021–202544014
2026under 10 wells1

Places in Bexar County with wells in this layer

Common questions

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

Home water wells that draw from the Upper Trinity in Bexar County, Texas are typically 350 to 650 feet deep (median 450 ft, 57 wells reported since 2001).

How many Bexar County wells draw from this layer?

It is a minor layer here: just 5% of the 394 wells the state's model covers; the main one is the Middle Trinity (89%). Only 37% 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 235 feet below the surface (43 wells).

What a well costs here

At the median depth for this layer in Bexar County (450 feet), a complete home well would cost roughly $14,000 to $33,500: $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 (350 to 650 feet) the range runs from $11,500 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 37% 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/upper-trinity. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.

Sources