Texas sits on nine major aquifers and twenty-one minor ones. Together they supply roughly half of the state’s water — and almost all of its rural drinking water. Where you live decides which one you’ll drill into, how deep your well will go, what your water will taste like, and how much it will cost. Below is a working guide for homeowners and well owners: depths, geography, yields, and what to expect from each.
Major aquifers
The Texas Water Development Board recognizes nine major aquifers — the ones that produce the most water and underlie the most ground. If you’re drilling a residential well in Texas, odds are very good you’re going into one of these.
The largest aquifer in the United States and the workhorse of Texas agriculture. Underlies most of the Panhandle. Famously declining — water levels have dropped more than 100 feet in parts of the southern High Plains since 1950. Most residential wells are 100–400 feet deep, though depth to water is rising every year.
A layered sand-and-clay system stretching from Louisiana to Mexico. Supplies most of Houston, Beaumont, Victoria, and the Coastal Bend. Land subsidence from over-pumping is a serious issue, especially around Harris and Galveston counties — which is why the Harris-Galveston Subsidence District exists.
One of the most productive karst aquifers on earth, and the most heavily regulated in Texas. Supplies San Antonio almost entirely and parts of Austin. Three zones — contributing, recharge, transition — each governed differently. The Edwards Aquifer Authority caps total pumping.
A long sandstone band running diagonally across East and South Texas. Known for high yields and good-quality water — among the best aquifers in the state for residential supply. Increasingly used for municipal water, including controversial export projects to the I-35 corridor.
A multi-layered system of sands and limestones that underlies a huge portion of central and north Texas. Where Edwards isn’t available, the Trinity is what Hill Country homeowners drill into. Yields vary enormously by sub-formation — Hosston/Travis Peak generally productive, Glen Rose temperamental.
A separate system from the Balcones Edwards — covers much of the area between San Angelo, Sonora, Junction, and the Pecos. Useful for ranching and rural homes but generally less productive than its Hill Country cousin. Water can be hard with elevated sulfates in places.
An alluvial aquifer along the Pecos River, used mostly for irrigation. Water quality varies widely — fresh near recharge zones, brackish to saline elsewhere. Oilfield activity is a major contamination concern.
A patchy collection of stranded alluvial deposits, not one continuous formation. Important locally for ag and rural homes around Haskell, Knox, and Baylor counties. High nitrates are a known problem.
Two adjacent basin-fill aquifers supplying El Paso and the lower Rio Grande Valley around the city. Fresh water is finite and the freshwater–saline interface is moving. El Paso has been a national leader in conservation and direct potable reuse partly because of this aquifer’s limits.
Minor aquifers
Smaller in extent or yield but locally indispensable. If you live above one of these, it may be the aquifer your driller targets — especially in deep East Texas, the Llano Uplift, and pockets of West Texas.
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