The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development of new technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume of MAR at global scale, and to illustrate the advancement of all the major types of MAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity of climate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research-on hydraulic design of facilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers-has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance of MAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km 3 /year,~2.4% of groundwater extraction in countries reporting MAR (or~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality of water supplies. Keywords Managed aquifer recharge. Artificial recharge. Review. Water banking. History of hydrogeology This article is one of a series developed by the International Association of Hydrogeologists (IAH) Commission on Managing Aquifer Recharge

The underground storage of treated drinking water results in the elimination of trihalomethanes (THMs) and haloacetic acids (HAAs) produced during treatment and in a decrease in the concentration of residual disinfection by‐product (DBP) precursors. Removal of THMs is associated with denitrifying conditions, whereas HAAs are removed under aerobic conditions. The findings are consistent with a biological mechanism for DBP and DBP precursor removal.

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San Antonio Water System (SAWS) developed its Aquifer Storage Recovery (ASR) program in the Carrizo aquifer to provide potable water supply reliability for San Antonio during droughts while protecting natural ecosystems and threatened and endangered species at Comal Springs and San Marcos Springs and augmenting downstream flows in the San Antonio River and estuarine ecosystems. It enables SAWS to completely optimize use of its Edwards Aquifer Withdrawal Permit with no wasted water, leveling out seasonal demand stresses on the Edwards aquifer. The SAWS Carrizo ASR wellfield recovery hydraulic capacity was designed to provide 64 million gallons per day (MGD) (0.24 Mm3/D). However, as built, the briefly tested recovery capacity, in practice, is approximately 80 MGD (Kirk Nixon and Kevin Morrison, verbal communication, 2022). Almost 200,000 acre feet (AF) (247 Mm3) of drinking water have been stored to date. The water recovered from storage requires only re‐disinfection prior to transmission and distribution to customers. During the period 2011 to 2014, a drought of near record intensity required SAWS to recover a total volume exceeding 50,000 AF (61.7 Mm3) over the 4‐year period. The ASR wellfield area and H2Oaks treatment facility serve as a central location for integration of two other long‐term water supply strategies including desalination of brackish groundwater from the underlying Wilcox aquifer and groundwater production from the local Carrizo aquifer. Several lessons have been learned during 18 years of ASR operation, as addressed in this article.