Middle Trinity: how deep the wells are
Home water wells that draw from the Middle Trinity in the Texas Hill Country are typically 365 to 615 feet deep (median 480 ft, 5,005 wells drilled in the last 10 years). In the state's model it is limestone and sand. It carries the most weight in Bexar County (89% of its wells), Medina County (77% of its wells) and Bandera County (75% of its wells). Estimated cost of a complete well at the median depth: $14,500 to $35,500.
Updated every day from Texas Water Development Board driller reports. Last update: November 11, 2026, using the state file of November 10, 2026.
Under Canyon Lake, Comal County
Dot: median. Bar: middle half (25th to 75th percentile). Counties with the most wells in this layer.
Digging in…
What this layer is
The Middle Trinity groups the lower member of the Glen Rose Limestone, the Hensell Sand and the Cow Creek Limestone. It is the layer most Hill Country home wells are completed in. Under it, the Hammett Shale separates it from the Lower Trinity.
Units the model puts in this layer: lower Glen Rose Limestone, Hensell Sand, Cow Creek Limestone.
Checked against the state's own aquifer codes: where our method names this layer, the state agrees in 85% of 1,503 wells.
Source of the layers: TWDB's Hill Country Trinity model, with 1 mile cells.
Key figures
- Typical depth (middle half)
- 365 to 615 feet
- Median depth
- 480 feet
- Deepest 10% are past
- 760 feet
- Water level (median)
- 265 feet
- 3,617 wells
- Yield (median)
- 25 gpm
- 4,075 wells, gallons per minute
- Wells used
- 5,005
- In the last 10 years
- All years on file
- 10,335
- median 470 ft, since 1982
- Confidence
- Standard (30 or more wells)
Counties where homes draw from this layer
Only counties with at least 10 wells in the layer. The share is of the county's wells that the model covers.
| County | Median depth (ft) | Wells | Share of the county's wells |
|---|---|---|---|
| Kendall County | 380 | 904 | 75% |
| Bandera County | 500 | 722 | 75% |
| Gillespie County | 318 | 676 | 51% |
| Comal County | 480 | 594 | 62% |
| Blanco County | 443 | 542 | 70% |
| Kerr County | 600 | 520 | 58% |
| Hays County | 500 | 495 | 57% |
| Bexar County | 700 | 349 | 89% |
| Medina County | 730 | 113 | 77% |
| Travis County | 325 | 90 | 10% |
Places where it is the main layer
- Canyon Lake 480 ft
- San Antonio 521 ft
- Bulverde 504 ft
- Lakehills 500 ft
- Fredericksburg 177 ft
- Timberwood Park 563 ft
- Wimberley 710 ft
- Boerne 589 ft
- Kerrville 580 ft
- Scenic Oaks 560 ft
- Cross Mountain 698 ft
- Bear Creek 650 ft
- Fair Oaks Ranch 462 ft
- Comfort 390 ft
- Grey Forest 780 ft
- Belterra 630 ft
- Driftwood 470 ft
- Blanco 405 ft
- Lake Medina Shores 460 ft
- Woodcreek 495 ft
- Ingram 520 ft
- Bandera 490 ft
Where it sits among the model's layers
From top to bottom, with the median depth of the home wells that draw from each:
| Layer (state's model) | Rock | Median depth (ft) | Wells |
|---|---|---|---|
| Edwards Group | limestone | 205 | 233 |
| Upper Trinity | limestone and marl | 245 | 467 |
| Middle Trinity | limestone and sand | 480 | 5,005 |
| Lower Trinity | sand and limestone | 510 | 1,875 |
Depth over time
New home wells in this layer are deeper than 20 years ago: the median went from 450 feet (2003 to 2007) to 500 feet (2021 to 2025), 11% more. Deeper wells do not always mean the water dropped: a driller may be going for another layer, better water or more reserve.
| Period | Median depth (ft) | Wells |
|---|---|---|
| 2001–2005 | 440 | 1,687 |
| 2006–2010 | 465 | 1,935 |
| 2011–2015 | 467 | 1,348 |
| 2016–2020 | 460 | 2,356 |
| 2021–2025 | 500 | 2,732 |
| 2026 | 487 | 264 |
Common questions
How deep is a well in the Middle Trinity?
Home water wells that draw from the Middle Trinity in the Texas Hill Country are typically 365 to 615 feet deep (median 480 ft, 5,005 wells drilled in the last 10 years).
What is the Middle Trinity?
The Middle Trinity groups the lower member of the Glen Rose Limestone, the Hensell Sand and the Cow Creek Limestone. It is the layer most Hill Country home wells are completed in. Under it, the Hammett Shale separates it from the Lower Trinity.
How deep does the water stand in these wells?
When the wells were finished, the water stood a median 265 feet below the surface (3,617 wells).
What a well in this layer costs
At the median depth for this layer (480 feet), a complete home well would cost roughly $14,500 to $35,500: $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 (365 to 615 feet) the range runs from $11,500 to $43,500. 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.
For 98% 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/formations/middle-trinity. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.
Sources
- Submitted Driller's Reports database, Texas Water Development Board (TWDB) (file of November 10, 2026)
- Groundwater Availability Model for the Hill Country portion of the Trinity Aquifer System, Texas. Jones, I.C., Anaya, R., and Wade, S.C., Texas Water Development Board, 2009, GAM v2.01 (MODFLOW-96). TWDB groundwater availability model.
- Ground elevation: Terrain Tiles (Mapzen), Registry of Open Data on AWS
- TWDB well report viewer (each well's official report)