"The storage of water in a well in a suitable aquifer during times when the water is available, and recovery of the stored water from the same well when needed."
ASR is the smart way to store water underground — using the earth's own geology as a natural reservoir, with no evaporation, no land clearing, and minimal environmental impact.
During rainy seasons, periods of low demand, or when treatment plant capacity exceeds distribution needs, surplus treated water is pumped down through the ASR well into a suitable aquifer far below the surface. The water is held there — safely and naturally — until it is needed.
During drought, peak summer demand, an emergency situation, or any time when supply falls short of demand, the stored water is pumped back up through the very same well — treated if necessary, then distributed to the water supply network. The cycle repeats as needed.
The basic concept of storing drinking water underground dates back hundreds of years or more, with origins likely in what is now Turkmenistan. Ancient civilizations understood intuitively that water could be pushed underground and retrieved. Modern ASR, however, transforms that ancient instinct into precision engineering — using carefully designed wells, rigorous water quality management protocols, and advanced hydrogeological science to achieve reliable, large-scale underground water storage that meets the demands of modern cities and infrastructure.
As shallow as 60 metres and as deep as 800 metres, depending on aquifer location and site conditions.
Fresh, brackish, saline, and seawater aquifers — ASR works across a wide range of underground water chemistry conditions.
Screened wells for sand aquifers; open borehole wells for limestone and volcanic aquifers. Construction adapted to geology.
From a single ASR well to massive wellfields. Designed to match the scale of the water supply challenge at hand.
In development: recovery capacity of 1.0 to 1.5 million cubic metres per day — enough for major metropolitan areas.
Horizontal Directionally-Drilled (HDD) ASR wells available for sites with special surface conditions or access constraints.
Traditional surface reservoirs remain vital infrastructure — but ASR wells offer significant complementary advantages. In many cases, combining both approaches delivers the most cost-effective path to water security.
| 🏞️ Surface Reservoir (Dam) | 💧 ASR Underground Storage |
|---|---|
| Very expensive to build and maintain | More economical; built incrementally as demand grows |
| Requires large tracts of land | Small surface footprint — only the wellhead above ground |
| Subject to evaporation and seepage losses | No evaporation losses — fully protected underground |
| Can face environmental and community opposition | Minimal land disruption and community opposition |
| Fills quickly from rainfall or surface runoff | Charges more slowly, but stores very large volumes |
| Exposed to algae growth and surface contamination | Protected underground from surface contamination |
Best practice: In many cases, combining aquifer storage with surface reservoir storage is the most cost-effective approach to achieving long-term water supply reliability and sustainability.
ASR Systems LLC has been evaluating and implementing ASR solutions since 2001. Contact David Pyne to discuss your project.