Which formation do Texas water wells draw from?
Of the 291,681 home wells with a depth in the state's reports, 204,803 (70%) fall inside a TWDB layered model this atlas has processed, across 141 counties. For those wells we estimate which layer the water comes from. Below are the layers of each model, shallowest to deepest, with the median depth of home wells in each.
Updated every day from Texas Water Development Board driller reports. Last update: November 11, 2026, using the state file of November 10, 2026.
Northern Trinity and Woodbine aquifers
Hydrogeology and Documentation of the Northern Trinity and Woodbine Aquifer System Groundwater Availability Model (NTGAM) (Ellis and others, 2025). 57,261 home wells in 62 counties fall inside this model, which uses quarter mile cells, summarized here to about 1.3 miles.
| Layer (state's model) | Rock | Median depth (ft) | Middle half (ft) | Wells |
|---|---|---|---|---|
| Above the Woodbine | shale, chalk and marl | 160 | 64–330 | 1,739 |
| Woodbine | sandstone with shale | 260 | 180–360 | 1,037 |
| Washita and Fredericksburg | limestone, marl and clay | 240 | 180–400 | 1,050 |
| Upper Trinity (Paluxy and Glen Rose) | sandstone, limestone and marl | 280 | 200–400 | 9,322 |
| Lower Trinity (Twin Mountains and Travis Peak) | sandstone with shale and limestone | 340 | 200–455 | 12,230 |
How well it works: In 7,977 wells in the area of the state's Northern Trinity and Woodbine model (North and Central Texas) 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 74% of them, and that layer or the one next to it in at least 95%; among the 3,130 of those wells that the state places in a Trinity layer (Paluxy to Hosston) it is about 56%.
- The layers come from the Texas Water Development Board's Northern Trinity and Woodbine model, with quarter mile cells, summarized here to about 1.3 miles. 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.
- In this model every layer is at least 30 feet thick, even where the real rock is thinner or missing. Thin layers and the edges of the model are approximate.
- Inside the Trinity this atlas does not name single model layers: it groups the Paluxy and Glen Rose (upper Trinity) and groups the Hensell, Pearsall and Hosston (lower Trinity, Twin Mountains and Travis Peak), because the check against the state's codes shows the method cannot separate them reliably.
Trinity Aquifer, Hill Country
Groundwater Availability Model for the Hill Country portion of the Trinity Aquifer System, Texas (Jones and others, 2009). 20,632 home wells in 16 counties fall inside this model, which uses 1 mile cells.
| Layer (state's model) | Rock | Median depth (ft) | Middle half (ft) | Wells |
|---|---|---|---|---|
| Edwards Group | limestone | 205 | 180–260 | 233 |
| Upper Trinity | limestone and marl | 245 | 185–340 | 467 |
| Middle Trinity | limestone and sand | 480 | 365–615 | 5,005 |
| Lower Trinity | sand and limestone | 510 | 420–658 | 1,875 |
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.
Gulf Coast Aquifer System, northern part
Northern Portion of the Gulf Coast Aquifer System Groundwater Availability Model for Groundwater Management Area 14 Joint Planning (GMA 14 Model) (Keester and others, 2025). 77,361 home wells in 51 counties fall inside this model, which uses cells of about 0.62 mile (1 km).
| Layer (state's model) | Rock | Median depth (ft) | Middle half (ft) | Wells |
|---|---|---|---|---|
| Chicot Aquifer | sand, silt and clay | 240 | 180–350 | 18,759 |
| Evangeline Aquifer | sand and clay | 215 | 174–267 | 5,066 |
| Jasper and Catahoula, with the Burkeville | sand, sandstone, clay and volcanic tuff | 230 | 170–304 | 5,628 |
How well it works: In 14,333 wells in the area of the state's northern Gulf Coast Aquifer model (Houston and Southeast Texas) where the State of Texas recorded the aquifer, the formation our method says the well draws from (as grouped on these pages) is the one the state recorded in about 83% of them, and that formation or the one next to it in at least 99%; of the 3,578 of those wells that the state records in the Evangeline, it names the Evangeline for about 51% and the Chicot for most of the rest.
- The layers come from the Texas Water Development Board's northern Gulf Coast Aquifer model, with cells of about 0.62 mile (1 km). It is a regional model, not a survey of any lot.
- The state's model has cells of about 3,277 ft (1 km, 0.62 mile); we read it on a grid of about 0.6 by 0.7 miles. It is not a survey of any lot, so we give ranges.
- Figures go by three groups: Chicot, Evangeline, and Jasper and Catahoula with the Burkeville. The state's records cannot tell the Burkeville, the Jasper and the Catahoula apart at a well (alone, the Burkeville matched 33% and the Catahoula 50%), so they are never named one by one as the formation of a well or a place.
High Plains Aquifer System (Ogallala, Edwards-Trinity, Dockum)
Numerical Model Report for the High Plains Aquifer System Groundwater Availability Model (Deeds and others, 2015). 49,549 home wells in 65 counties fall inside this model, which uses half mile cells, read here on a grid of about 1.2 by 1.4 miles.
| Layer (state's model) | Rock | Median depth (ft) | Middle half (ft) | Wells |
|---|---|---|---|---|
| Ogallala Aquifer | sand, gravel, silt and caliche | 161 | 125–258 | 12,389 |
| Pecos Valley Aquifer | sand, gravel and clay | 180 | 131–267 | 90 |
| Edwards-Trinity and Rita Blanca (Cretaceous rock under the Ogallala) | sand, sandstone and limestone | 163 | 110–205 | 5,214 |
| Dockum Group | red mudstone, sandstone and conglomerate | 250 | 165–440 | 6,009 |
How well it works: In 22,814 wells in the Texas part of the state's High Plains Aquifer System model (the Panhandle, the South Plains and the Permian Basin) where the State of Texas recorded the aquifer, the formation our method says the well draws from (as grouped on these pages) is the one the state recorded in about 75% of them; when it names the Dockum (4,542 wells), the state's record agrees only about 33% of the time, and most of the others are recorded as Ogallala wells.
- The layers come from the Texas Water Development Board's High Plains Aquifer System model, with half mile cells, read here on a grid of about 1.2 by 1.4 miles. It is a regional model, not a survey of any lot.
- The state's model has half mile cells; we read it on a grid of about 1.2 by 1.4 miles, Texas part only. Layers from version 1.01 (2015); the 2025 extension (1.02) did not change them. It is not a survey of any lot, so we give ranges.
- Figures go by four groups: Ogallala; Pecos Valley; Edwards-Trinity and Rita Blanca (Cretaceous rock under the Ogallala; the Rita Blanca alone matched the state 19%); Dockum (upper and lower together: the state's codes almost never say which). The Edwards-Trinity group joins three aquifers in different places (High Plains around Lubbock, Plateau around Midland and Odessa, Rita Blanca in Dallam and Hartley): county and place pages name the local one where they can.
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.
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. License CC BY 4.0. https://doi.org/10.5281/zenodo.24126380.