EDWARDS AQUIFER

The Edwards Aquifer: J-17 levels, drought stages and pumping limits, explained

How the Edwards Aquifer works, why it reacts so fast to drought, what the J-17 index well measures, and how Edwards Aquifer Authority stages cut permitted pumping by 20–44%.

By Argos Tellus · Updated October 2, 2026

KEY TAKEAWAYS

The Edwards Aquifer is a karst limestone aquifer in south-central Texas and the primary water source for San Antonio and much of the surrounding region. In 1975 it became the first aquifer in the U.S. designated a sole source aquifer by EPA.
The Edwards Aquifer Authority (EAA) caps total permitted withdrawals at 572,000 acre-feet a year to protect springflow — and the endangered species — at Comal and San Marcos springs.
In drought, EAA critical period stages for the San Antonio pool are triggered by the J-17 index well’s 10-day average level (below 660, 650, 640, 630 and 625 feet above sea level) or by low springflow.
Each stage cuts permitted withdrawals: 20% at Stage 1, 30% at Stage 2, 35% at Stage 3, 40% at Stage 4 and 44% at Stage 5.
The San Antonio pool reached Stage 5 in 2025 and has moved between stages since — so any Edwards-dependent water supply has to be planned around regular, deep cuts.

What makes the Edwards Aquifer different

The Edwards (Balcones Fault Zone) Aquifer is made of fractured, cavernous limestone. Rain and streamflow sink into it rapidly across the recharge zone on the edge of the Hill Country, travel through conduits, and discharge at large springs such as Comal Springs in New Braunfels and San Marcos Springs. That karst plumbing makes it one of the most productive aquifers in the U.S. — and one of the fastest to respond to drought.

Unlike the slow, thick Ogallala, the Edwards can rise tens of feet after a wet season and fall just as quickly in a dry one. Water availability from it is therefore governed less by long-term storage than by drought rules that cut pumping as levels and springflow drop.

The Edwards Aquifer Authority and the 572,000 acre-foot cap

The Texas Legislature created the Edwards Aquifer Authority in 1993 to manage pumping and protect springflow after federal litigation over endangered species that live in the springs. EAA permits groundwater withdrawals up to a statutory total of 572,000 acre-feet a year for municipal, industrial and irrigation use.

Unlike most Texas groundwater, which is regulated by local groundwater conservation districts, Edwards rights are capped, permitted and transferable — a market in which the reliability of each acre-foot depends on how often drought stages cut it.

J-17 index well and critical period stages

For the San Antonio pool, EAA uses the J-17 index well in San Antonio and the springflow at Comal and San Marcos springs as triggers. A more restrictive stage starts when any indicator’s 10-day average crosses its threshold; stepping back down requires all indicators to recover.

Stage (San Antonio pool)	J-17 10-day average below	Cut to permitted withdrawals
Stage 1	660 ft above mean sea level	20%
Stage 2	650 ft	30%
Stage 3	640 ft	35%
Stage 4	630 ft	40%
Stage 5	625 ft	44%

What drought stages mean for water users

Cuts apply to permit holders authorized to pump more than three acre-feet a year — cities and water utilities, industry and agriculture. During a long drought, an Edwards permit can deliver little more than half its face value for months at a time. In 2025, the San Antonio pool reached Stage 5, the deepest level of cuts; check EAA for the current stage.

Utilities hedge with other supplies — other aquifers, surface water, aquifer storage and recovery, desalination and conservation. For a new large user, such as a manufacturing plant or a data center, the practical question is not the permit’s face value but its firm yield in a repeat of the worst drought on record.

Protecting the recharge zone

Because water enters the Edwards quickly through fractures and sinkholes, contamination on the recharge zone can reach the aquifer with little natural filtering. Development over the recharge and contributing zones is regulated by the Texas Commission on Environmental Quality’s Edwards Aquifer rules, and local governments have purchased conservation land over the recharge zone to protect both water quantity and quality.

Frequently asked questions

What is the J-17 well?

The J-17 index well in San Antonio is the Edwards Aquifer Authority’s benchmark well for the San Antonio pool. Its 10-day average water level, along with springflow at Comal and San Marcos springs, triggers drought (critical period) stages.

What are the Edwards Aquifer drought stages?

For the San Antonio pool, Stage 1 starts when the J-17 10-day average falls below 660 feet above sea level, Stage 2 below 650, Stage 3 below 640, Stage 4 below 630 and Stage 5 below 625 — or when springflow drops below set thresholds.

How much do Edwards Aquifer drought stages cut pumping?

Permitted withdrawals are cut by 20% in Stage 1, 30% in Stage 2, 35% in Stage 3, 40% in Stage 4 and 44% in Stage 5 for the San Antonio pool.

How much water can be pumped from the Edwards Aquifer?

The Edwards Aquifer Authority permits up to 572,000 acre-feet a year in total, before drought-stage reductions.

Why does the Edwards Aquifer drop so fast in drought?

It is a karst limestone aquifer with large conduits, so it recharges and drains quickly. Levels respond within weeks to rainfall, pumping and springflow, unlike thick, slow aquifers such as the Ogallala.

HOW ARGOS HELPS

Phreatic — groundwater availability

A dedicated Edwards model among its per-aquifer forecasters, with water-level forecasts out to 20 years.

CARI — aquifer reasoning agent

Ask how drought stages and J-17 trends affect a site’s supply, in plain English.

SOURCES

Figures are taken from the primary sources above and dated as of the update shown. Concentrations are expressed in mg/L. Spot an error? Email support@argostellus.com.

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