Managed Aquifer Recharge for Sustainability. Experiences from UNAM Water Network

INTRODUCTION
Groundwater are essential for human consumption, food production, and ecological stability. Their distinctive feature—that they are not visible to the naked eye like lakes and rivers—has direct implications for management: they are outdated in monitoring, economic valuation, institutional design, and regulatory compliance. In practice, this has resulted in extraction patterns that exceed natural recharge, with cumulative effects that manifest themselves as piezometric diminishing (decrease in quantity), degradation of quality, saline intrusion into coastal aquifers, loss of base flows, and subsidence (sinking) of the land. In this framework, Managed Aquifer Recharge (MAR) has consolidated as a high-impact strategy within sustainable management portfolios: it does not replace regulation, demand reduction nor efficiency, but it can increase storage, improve resilience to droughts, and, in certain schemes, contribute to the natural attenuation of pollutants (Dillon et al., 2022).

This article presents an overview of the state of groundwater globally and in Mexico: an analytical description of the MAR as a comprehensive strategy to promote water security and the contributions of the UNAM Water Network to the subject.

Infiltration lagoon, Sonora.

 Jorge Alberto Arriaga Medina

GROUNDWATER IN THE WORLD: GROWING DEPENDENCE AND GOVERNANCE GAPS
On a global scale, the available evidence is clear: there is a structural and growing dependence on groundwater, particularly for domestic and agricultural uses. According to various agencies of the United Nations, groundwater contributes approximately half of the volume of domestic use and about a quarter of the water withdrawn for irrigation.

Its importance in economic activities and in the fulfillment of the human right to water contrasts with the persistence of important gaps: hydrogeological information, monitoring networks, effective regulatory frameworks, and institutional capacities to assign, measure, verify, and adjust withdrawals based on sustainability objectives. As a result of these challenges, aquifer depletion is observed in multiple regions, associated to demand pressures, such as population growth, agricultural intensification, or urbanization, but also with emerging factors such as climate variability and the recurrence of prolonged droughts that increase dependence on “underground storage” as a source of buffering.

The impacts of sustained reduction are particularly relevant because of their cumulative and, in some cases, irreversible nature. Subsidence due to sediment compaction can compromise infrastructure and increase vulnerabilities to flooding; saline intrusion in coastal areas can limit its use for human consumption or irrigation, and quality degradation by nitrates, arsenic, or other contaminants introduces increasing treatment costs or restrictions on use. This is why contemporary approaches to sustainability have insisted on integrating groundwater management with surface water management, land use, and territorial planning, avoiding treating the aquifer as an isolated source of supply and acknowledging it as part of an integrated hydrological system.

 Ilustration: Monserrat García Silva

MEXICO: THE PRESSURE OF OVEREXPLOITATION
The discussion on groundwater sustainability in Mexico is part of a context of high climatic heterogeneity and strong urban concentration. In administrative and hydrogeological terms, the country recognizes 653 aquifers; the CONAGUA recognizes that 114 of them are overexploited, accompanied by associated problems such as saline intrusion and salinization in a subset of systems. This information implies that in a significant fraction of the hydrogeological territory, more water is extracted, in a sustained manner, than is recharged in the long term (CONAGUA, 2023).

Overexploitation is usually related to three factors:

1. The increase in agricultural and urban demand with historical incentives aimed at sustaining supply. 
2. Urban expansion that reduces or alters natural recharge zones and increases overflow. 
3. The asymmetries in control, measurement, and compliance capacities. 

Added to this are quality challenges: diffuse pollution associated with agricultural fertilization; discharges, and the mobilization of natural constituents by changes in hydraulic gradients. In this framework, MAR is recognized as a strategy with great potential, but requiring enabling conditions: technical criteria for selecting sites and devices, sanitary guarantees, operation and maintenance mechanisms, and incentive schemes and allocation of benefits that prevent recharging from being a no-return cost for those who implement it. 

Participants of the 9th International Symposium on Aquifer Recharge Management.

 Jorge Alberto Arriaga Medina

MAR: OPERATIONAL DEFINITION, MODALITIES, AND PERFORMANCE CONDITIONS
MAR is understood as increasing aquifer recharge above natural infiltration, through interventions designed to improve storage and, in certain cases, quality. Its implementation admits a variety of configurations: lagoons or infiltration channels, induced recharge from riverbeds, injection wells, retention and infiltration structures, and schemes coupled to the reuse of treated water through soil-aquifer treatment processes (Escolero, Gutiérrez & Mendoza, 2017).

Due to its diversity, MAR is usually characterized not as a technique, but as a set of solutions that depend on at least three elements:

1. Objective: to reduce reductions, control subsidence, increase seasonal storage, generate hydraulic barriers against saline intrusion or improve flood control.
2. Hydrogeological environment: permeability, transmissivity, storage, presence of confined or semi-confined aquifers.
3. Water source: rainwater, surface or treated waste, considering quality and variability.

With these elements in mind, contemporary designs of MAR emphasize its socio-technical character. In other words, in addition to engineering, a clear regulatory framework is required, a robust governance system that manages who recharges, who monitors, and who responds to incidents, and an information system that allows performance to be evaluated and practices to be adjusted. 

UNAM WATER NETWORK: FROM CONSENSUS BUILDING TO POLICY GUIDELINES AND TECHNICAL CAPACITIES
For UNAM, studying and proposing solutions in MAR is not a thematic choice: it is a logical consequence of its role as a public institution that produces knowledge, trains specialists, disseminates scientific culture, and leads capacities towards the solution of national problems. In this sense, UNAM Water Network (RAUNAM) has operated as a platform that articulates knowledge, evidence, and social dialogue so that groundwater ceases to be an “invisible” resource in decision-making and becomes a field of action with verifiable criteria.

UNAM WATER NETWORK HAS OPERATED AS A PLATFORM THAT ARTICULATES KNOWLEDGE, EVIDENCE, AND SOCIAL DIALOGUE SO THAT GROUNDWATER CEASES TO BE AN “INVISIBLE” RESOURCE IN DECISION-MAKING

RAUNAM promotes the integration of multidisciplinary and multi-scale university capacities to understand water challenges and translate them into concrete policy, technology, and management proposals. MAR fully fits into this mission because it requires a combination of at least hydrogeology, water quality, engineering, economics, law, and governance. RAUNAM’s contribution to the MAR, therefore, cannot be understood solely as a sum of projects or events; it must be read, above all, as a university response to a structural problem in the country.

Perhaps one of the most significant contributions of RAUNAM was the organization in Mexico of the 9th International Symposium on Aquifer Recharge Management (ISMAR), recognized as the main global event on research and practice in MAR. It is a space of convergence between science, practice, and regulation and covers the complete cycle of projects, from design and construction to operation, maintenance, monitoring, modeling, regulation, and economic evaluation (UNAM, IINGEN, CONAGUA, 2016). 

The activity brought together 23 countries from the five continents, with 200 participants, 83 presentations, two keynote speeches, three courses and four workshops, and had as its central result the approval of the Policy Guidelines for Sustainable Groundwater Management. There are six postulates that go beyond a list of aspirations; they structure a public policy reasoning that links the nature of the resource with the instruments required for its sustainability. Following we summarize the guidelines (González & Arriaga, 2019):

1. It establishes the relevance of aquifers for water and food security, emphasizing their status as a common resource and their exposure to emerging pressures such as climate change, population growth, and urbanization. 
2. It introduces an operational notion of sustainability aimed at defining time horizons and goals to restore the balance between extraction and recharge, recognizing that the inertia of the system requires long-term planning. 
3. It places knowledge as an enabling condition: aquifers are unique and complex systems; therefore, greater investments are required in characterization, monitoring, tools, and technologies, as well as in the dissemination of information and the training of specialized human resources. 
4. It emphasizes the concept of integrality, understood as the need for a clear regulatory framework, institutions with the capacity to enforce the law, multilevel co-responsibility, and a portfolio of actions that combine reuse, rainwater harvesting, demand reduction, water transfers where relevant, and the MAR. 
5. It explicitly positions the MAR as a key component for sustainability, recommending incentives and specialized training, and warning of the need to implement MAR where suitable aquifers and conditions exist to justify costs and ensure their performance. 
6. It incorporates participation as a permanent requirement. Given the common nature of the resource, social acceptance, trust, and compliance are strengthened through significant involvement of diverse actors, linked to decision-making and sustained over time. 

In parallel to this international framework, RAUNAM has contributed through technical-institutional coordination actions: the formation of an analysis group on managed aquifer recharge, the development of an inventory of MAR projects, the preparation of a preliminary recharge project through infiltration lagoons in the Sonora River basin, the implementation of a pilot test in the Chihuahua-Sacramento geohydrological basin, and the promotion of capacities through technical conferences and specialized workshops. Together, these actions seek to systematize evidence, reduce technical uncertainty, build capacities, and translate findings into decision-making criteria.

THE VALLEY OF MEXICO: AN EMBLEMATIC CASE
The Metropolitan Area of the Valley of Mexico concentrates about 20 percent of the country’s population and 30 percent of its economic activity. Under these considerations, the distribution and regulation capacity of the urban system will continue to require the aquifer as the main source of supply. This is a sign of a dependence that becomes problematic when the aquifer reproduces the “tragedy of the commons:” multiple individual withdrawals, immediate benefits, deferred costs, and cumulative deterioration that is expressed, among other ways, in subsidence and damage to infrastructure (Spiliakos, 2024).

In response to its mission of contributing to the solution of the main national problems, RAUNAM and UNAM’s Institute of Engineering designed the Integrated Management and Managed Aquifer Recharge Plan for the Valley of Mexico under a strategic vision: the aquifer is a critical, finite, valuable, and vulnerable asset.

Frontal aerial view of infiltration lagoons for artificial aquifer recharge.

 Jorge Alberto Arriaga Medina

The plan organizes actions through a logic that articulates diagnosis, modeling, scenarios, and programs. Among the strengths of its approach is that it does not assume a single future. In their structure, the scenarios organize uncertainty based on factors such as population, economic growth, governance, technology, and environment, and separate two trajectories: a desirable program under a sustainable scenario and an inertial program under an adverse scenario. The distinction is methodologically relevant because it avoids the common mistake of treating sustainability as an automatic result of building more infrastructure.

In the desirable program, the increase in supply is accompanied by efficiency in systems, reduction of losses, reuse, and increase in natural and artificial recharge. At the same time, in the inertial program, demand grows with the same consumption patterns, without an effective increase in supply, with persistent losses, reuse does not scale, extraction increases, and both natural and artificial recharge are eroded, with which the gap deepens.

The plan also operates with a 25-year horizon and includes supply components, but, above all, a reorganization of the portfolio so that sustainability does not depend on a single source of supply.

Another distinctive component of the Valley of Mexico’s strategy is not only hydraulic but also institutional and fiscal. The plan proposes measures aimed at correcting a typical imbalance in MAR: requiring investment, operation, and monitoring from those who recharge, but not offering verifiable benefits or cost recovery mechanisms. Among the lines of action are: promoting reforms that allow concessions to recognize a part of the volume recharged; introduce tax credits for recharge; reviewing recharge water quality criteria so that they are demanding in risk control and operable in practice, and eliminating tariff distortions that, in contexts of overexploitation, end up subsidizing unsustainable trajectories.

Infiltration lagoons.

 Jorge Alberto Arriaga Medina

Added to this is a governance axis. The plan proposes to strengthen institutional capacities and articulate coordination instances at various scales with functions ranging from issuing guidelines for management and recharge plans, supervising their development, establishing priorities, and promoting their implementation, to intensifying communication and coordination with state governments, municipalities, operating agencies, farmers, and users.

In the technical component, the plan articulates recharge in two main aspects: natural recharge, which involves the protection and recovery of territorial conditions that allow infiltration, and recharge managed through specific projects. Here the strategic value is that recharge ceases to be a complement and becomes a program with the identification of specific opportunities. The proposal includes potential projects linked to existing infrastructure and available sources, particularly wastewater treatment plants as nodes to enable recharge under quality control schemes and devices such as infiltration or recharge wells in selected areas. 

GROUNDWATER SUSTAINABILITY IS NOT A SPONTANEOUS RESULT OF THE HYDROLOGICAL BALANCE, BUT AN INSTITUTIONAL PRODUCT SUPPORTED BY INFORMATION, CAPACITIES, AND COMPLIANCE MECHANISMS

FINAL THOUGHTS
The global analysis and the Mexican case converge on one premise: groundwater sustainability is not a spontaneous result of the hydrological balance, but an institutional product supported by information, capacities, and compliance mechanisms. In this framework, MAR constitutes a technically viable and strategically relevant strategy, but conditioned by criteria for site selection, quality of sources, operation and maintenance, monitoring, and incentive arrangements that allow it to be sustained over time. The contributions of UNAM Water Network, particularly the international and conceptual articulation expressed in the guidelines approved in ISMAR 9, and the translation of principles into operational criteria in the Valley of Mexico, show a trajectory that links evidence, training, and public policy.

In this sense, a National Program of Aquifer Recharge, supported by technical standards, financing schemes, and systematized public information, could become one of UNAM’s main contributions to address this growing challenge that is not exclusive to the Valley of Mexico or the country.

Water dispenser at UNAM.

 PUMAGUA

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