Aquifer storage, recovery, & recharge

Aquifer storage and recovery (ASR) and managed aquifer recharge (MAR) increase groundwater levels by supplementally recharging groundwater. ASR and MAR can help increase the availability of water during the summer by capturing and storing water during cooler months, when streamflows are high and water demands are low.

Groundwater is an important resource

Groundwater is critically important in Washington. ​Total groundwater use in the state is nearly 1.5 billion gallons per day.

  • More than 3.5 million people drink groundwater.
  • It is used to irrigate over 320,000 acres each year.
  • It is necessary for livestock, aquaculture, mining, and industrial purposes.
  • The natural discharge of cool groundwater is also critical for fish and other aquatic life.

In a few areas in the state, long-term declining groundwater levels indicate that more water is being withdrawn than is naturally recharged. A growing population and changing climate will likely continue this trend. Finding opportunities to capture and store water when it is available — so it can be used later in the year when surface water is limited — is becoming increasingly important.

Aquifer storage and recovery

Aquifer storage and recovery (ASR) has proven to be a cost-effective way to capture and store water when it is available so it can be used during times when it is limited. Groundwater storage can serve the same purposes as surface water reservoirs, without many of the issues and costs associated with dams.

The number of projects in Washington is growing, and they vary widely in size and scale. ASR can be used in places where surface storage is not practical or economically possible, including urban, industrial, and residential areas.

Other recognized benefits include:

  • Large quantities of water can be stored underground, reducing the need to construct large and expensive surface reservoirs.
  • ASR systems are considered to be more environmentally friendly than surface reservoirs.
  • Aquifer storage offers more protection from tampering than surface storage.
  • The practice may stabilize or reverse declining water levels in an aquifer that has experienced long-term declines due to heavy pumping.

ASR application process

We can accept a single reservoir application form covering both storage and use of the stored water.

Before you apply

Assess potential issues and impacts to the hydrogeologic system and the environment. Refer to Chapter 173-157 WAC for more details. 

If the general setting and conditions cannot be provided with the application, then you must complete a more detailed feasibility study. The feasibility study should provide information to characterize the hydrologic system, reduce uncertainty with respect to project issues and impacts, as well as better quantifying the available storage potential within the aquifer.

Complete and submit a pre-application consultation form, and schedule a meeting with us to discuss the project plan and likely requirements for monitoring and mitigation.

Submitting your application

Your application for an ASR project must contain, at a minimum:

  • Identification of the water rights for the source waters to be used for storage
  • A general description of the physical and operational designs of the hydrogeologic system, prepared by an engineer or geologist registered in the state of Washington
  • A project operation plan
  • A data monitoring plan
  • An environmental assessment and analysis of any potential adverse conditions or potential impacts to the surrounding environment that might result from the project; a mitigation plan must be included to address any such conditions or impacts

ASR Regulations

  • RCW 90.03.370 — Defines “reservoir” to include "any naturally occurring underground geological formation where water is collected and stored for subsequent use as part of an underground artificial storage and recovery project." This legislation allows us to issue reservoir permits to authorize ASR projects.
  • Chapter 173-157 WAC — Establishes standards for review of ASR proposals and for mitigating any adverse impacts in the following areas:
    • Aquifer vulnerability and hydraulic continuity
    • Potential impairment of existing water rights
    • Geotechnical impacts and aquifer boundaries and characteristics
    • Chemical compatibility of surface and ground waters
    • Recharge and recovery treatment requirements system operation
    • Water rights and ownership of water stored for recovery environmental impacts
  • Chapter 173-200 WAC — Establishes that water to be stored in an aquifer as part of an ASR project must meet water quality standards for groundwaters of the state of Washington.
  • Chapter 90.48 RCW (Water Pollution Control Act) and Chapter 173-218 WAC (Underground Injection Control Program) - Require that injection wells for an ASR project be registered with us.

Managed aquifer recharge 

Managed aquifer recharge (MAR) shares elements with ASR, but is not intended for storage and subsequent recovery.

MAR supplements the natural pattern of recharging groundwater, which typically comes from rain and snow seeping into the ground. Because surface water and groundwater are connected, MAR can help add to the water discharging to streams and rejuvenate wetlands and springs. MAR can be an important tool for stabilizing or reversing declining groundwater levels. In some circumstances, it may be used as mitigation for other water withdrawals.

How it works

MAR projects release water on or near the surface above the local water table. Recharge is done, typically on a seasonal basis, by diverting surface water into infiltration sites. Sites can be natural or man-made, such as fields, gravel pits, ponds, canals, ditches, and shallow wells.

Sites must be chosen carefully and evaluated for potential infiltration rates and volumes as well as anticipated hydrologic and water quality effects resulting from the project. Suitable sites have permeable material at the surface and a water-table deep enough to allow levels to rise without causing problems, such as flooding.


A reservoir permit is usually not needed for MAR projects because water is not stored and actively recovered. However, a water right authorizing the diversion of surface water prior to recharge is required.

MAR projects can be expensive but are frequently cost-effective compared to alternatives. Costs include:

  • Acquiring or obtaining access to recharge sites
  • Site characterization
  • Construction
  • Monitoring
  • Water quality testing
  • Operation and maintenance
  • Reporting
  • P​ermitting

Cost impacts

  • Using existing facilities and infrastructure, such as an existing irrigation canal with a willing landowner, can significantly reduce costs.
  • Project objectives will affect costs. For example, an MAR objective commonly includes increasing flows in a nearby stream at the low-flow time, several months after water is available for recharge. This could significantly limit suitable sites, affecting project costs.