All about ASR: understanding aquifer storage and recovery as a water supply strategy Posted on April 9, 2025

We’re all familiar with piggy banks and savings accounts, right? You put your money into a bank for safekeeping, then withdraw it when needed. What if there was a way for communities to store water when it’s plentiful so they have access to it in times of emergency or drought?  

That’s the idea behind aquifer storage and recovery (ASR). It’s a way to stash excess water underground and pump it back up when supplies run low. In drought-prone states like Texas, ASR is becoming a critical water management strategy that helps communities avoid shortages. But how does it work? And how can more communities incorporate an ASR system into their operations? 

How ASR works 

ASR as a concept is simple: utilities and water providers store  water underground in an aquifer when supply exceeds demand, then pump it back up for use as needed. From engineering the systems to the science behind them, building and maintaining a functional ASR system isn’t quite so easy.  

Selecting a project site 

Not all underground geologic formations can serve as a piggy bank for water, so finding a suitable location is the critical issue for any new ASR system. That’s why, in 2019, the 86th Texas Legislature directed the Texas Water Development Board (TWDB) to investigate ASR and aquifer recharge with two specific directives: conduct a statewide suitability survey—which was published in 2020—and perform ASR studies for interested persons across the state.  

Generally, this is what the studies look for:  

• Porous rock layers, like sandstone or limestone, that allow water to flow in and out 

• Geological barriers, like clay layers, that prevent stored water from escaping 

• The mineral content, to avoid chemical reactions with injected water 

While these conditions are relatively straightforward, aquifer selection and implementation of ASR systems is complicated. It requires geologists and engineers to perform aquifer characterization studies to determine the most suitable area to store the water, then engineer the system (and its maintenance) to meet the goals of the project.  

Preparing the water and making it safe to store 

In Texas, surface water, groundwater, and reclaimed water have all been used in ASR systems. And, regardless of the source, the Texas Commission on Environmental Quality’s (TCEQ) regulations require that an ASR system cannot alter the quality of the native groundwater to a degree that would be harmful to people, animals, vegetation, or property, or require an unreasonably higher level of treatment than the native groundwater.  

So, before water is stored in an aquifer, it must be treated to ensure that it can be stored safely. These treatments include removing organic matter to prevent bacterial growth underground, balancing the pH and minerals so that the water doesn’t react with the aquifer, and filtering out particles to avoid clogging injection and extraction wells.  

Getting the water underground 

After it’s treated, ASR systems use injection wells to get the water underground, which typically double as extraction wells when it’s time to recover the water. These high-capacity wells send water hundreds or thousands of feet down, while pressure sensors ensure water spreads evenly through the rock, and monitoring wells are used to track where the water goes to prevent leaks. 

Injection is accomplished in two stages. The first stage establishes a buffer zone with the native groundwater, followed by injection of the retrievable water. Once injected, the water slowly spreads through tiny pores in the rock.  If the soil at the surface is impermeable and the aquifer is shallow, vadose zone wells can be used. This type of well is typically a large diameter that penetrates through the impermeable soil to layers where water can infiltrate the soil and drain into the aquifer. Unlike a reservoir, there’s no evaporation loss because ASR systems are sealed, natural storage systems.

Recovery: Pumping the water back up 

When drought hits, communities with ASR systems can pump the stored water back to the surface. After that, they can retreat the water if needed before distributing the water into the regular supply. Note, however, that recovery efficiency varies—while water injected to establish the buffer zone is not recoverable and some water may drift from storage due to hydraulic gradients, most of the stored water is available for recovery over the life of a project. 

The TWDB and Texas communities are leaning into ASR 

Texas knows the pain of drought, and with dry spells lasting longer and becoming more severe, ASR offers advantages for communities looking to explore options that will help secure their excess water supplies.  

While ASR requires significant up-front investments, it’s generally less expensive overall than constructing new infrastructure, and because well footprints are a fraction of the size of alternatives, the pre-existing land use can continue after the ASR system is installed. Furthermore, traditional reservoirs typically lose an average of around 7.2 million acre-feet of water each year due to evaporation and wind, which underground storage does not. 

There are currently eight authorized ASR systems in Texas, and 27 additional ASR projects were recommended in the 2022 State Water Plan. The TWDB has already completed an aquifer characterization for Guadalupe-Blanco River Authority and well longevity assessment for City of Bandera—and is in the process of publishing a new ASR suitability survey for the Lower Valley Water District in El Paso County and performing an aquifer characterization for the San Jacinto River Authority in Montgomery County due to growing interest in ASR around the state.  

If implemented, the 27 projects recommended in the state water plan are estimated to provide an additional 193,000 acre-feet of new water supply by 2070. Although ASR can’t solve all our state’s water management challenges, it’s a powerful alternative for communities to consider while diversifying their water supply portfolios and helping secure Texas’ water supply for the future. For more information about aquifer storage and recovery, visit the TWDB website.  

This article is posted in Aquifers / Water Planning / Technology / Water Supply .