Water scarcity, climate change, population growth and rising infrastructure costs have opened the door for unconventional or ‘new’ water sources. Reclaimed water reuse has historically been practised for potable use in the United States as de facto water reuse or unplanned indirect water reuse. The increasing number of planned indirect water reuse projects in the country and the approval of the first direct potable reuse projects have exposed the limitations of the regulatory system at the national and state levels. These limitations pose barriers and/or add uncertainty to the viability of potable water reuse.

Over the last decade, transboundary aquifers traversing the Mexico‐Texas border have generated growing interest of federal institutions on the Mexico side and state and federal institutions on the Texas side. Notwithstanding this, binational efforts to understand, assess, and manage shared groundwater resources remain limited and politically sensitive. On the Mexico side, long‐standing centralized groundwater governance structures have created institutional barriers at the local level to the expansion of knowledge and cooperation over these transboundary resources. On the Texas side, property rights related to groundwater resources limit the scope of options available for cooperative management of cross‐border aquifers. This paper examines stakeholders' perspectives on the borderland between Mexico and Texas through 44 surveys and personal interviews. Findings show that stakeholders appear to support a binational groundwater agreement as a means for assuring the sound long‐term management of transboundary groundwater resources in the border region; however, the majority of stakeholders also suggest that short‐term local or regional arrangements may be preferable over binational agreements as local/regional approaches may be more achievable or realistic. Second, participants identified leadership and individual personalities as key factors for success at the local level but noted that such influence had limited sustainability and limited regional‐systemic effects. Third, the stakeholders indicated that water quality, rather than water quantity, is the main driver of transboundary cooperation efforts in the region. Fourth, participants suggested that failures and successes in groundwater cooperation efforts are based more on fear and political lobbying than on understanding of scientific facts.

In 2016, research suggested there might be up to 36 transboundary aquifers located along the border between Mexico and the U.S. The main contribution of this study was to put together the available segments already existent in the literature without considering the validity of the criteria used to define the boundaries of those segments. In 2018, updated research reported 33 hydrogeological units (HGUs) crossing the boundaries between Mexico and Texas. This later analysis included the homogenization of geological nomenclatures, standardization of geological and hydrogeological criteria, using a specific methodology to correlate, identify, and delineate each HGU. The purpose of this paper is to use this latter methodology and expand the same analysis to include the transboundary aquifers between Baja California/California, Sonora/Arizona, and Chihuahua/New Mexico. Results of this study indicate that a total of 39 HGUs have been identified in this region which accounts for an approximate shareable land of 135,000 km² where both countries share half of the area. From the total shareable area, around 40% reports good to moderate aquifer potential and water quality, of which 65% is in the U.S. and 35% on the Mexico side. Border-wide, the total number of HGUs in the border region between Mexico and the United States is 72, covering an approximate area of 315,000 km² (180,000 km² on the U.S. side and 135,000 km² on the Mexico side). The total area that reports good to moderate aquifer potential as well as good to regular water quality ranges between 50 and 55% (of which approximately 60% is in the U.S. and the rest in Mexico).

The Hueco Bolson aquifer is a binational aquifer shared by the United States of America (USA) and Mexico that is strongly interconnected with the transboundary river, Rio Grande/Rio Bravo. Limited recharge, increasing urbanization, and intensified agriculture have resulted in the over-drafting of groundwater resources and stressed the aquifer, threatening its sustainability if mitigation actions are not taken soon. Research indicates that the aquifer’s hydraulic gradients and flow directions have changed due to the high groundwater withdrawal rates from the two major cities—El Paso (USA) and Ciudad Juarez (Mexico). This paper presents a comprehensive overview of the Hueco Bolson aquifer modeling history and makes a case for future modeling and binational engagement efforts. First, we discuss the evolution of groundwater modeling for Hueco Bolson from the past to recent times. Second, we discuss the main water management issues in the area, including water quality and quantity, stakeholders’ participation, and climate change. To address the challenges of holistic water management, we propose developing a graphical quantitative modeling framework (e.g., system model and Bayesian belief network) to include experts’ opinions and enhance stakeholders’ participation in the model. Though the insights are based on a case study of Hueco Bolson, the approaches discussed in this study can provide new strategies to overcome the challenges of managing a transboundary aquifer.

Shortly after being confirmed by the U.S. Senate in 2021, Commissioner Maria Elena Giner called for input into issues of importance to the U.S. Section of the International Boundary and Water Commission (USIBWC). Responding to her call, a group of border scholars committed to producing a white paper entitled “Water Management on the U.S.-Mexico Border: Achieving Water Sustainability and Resilience through Cross-Border Cooperation”. This document was presented to Commissioner Giner at the spring 2022 ABS Annual Meeting in Denver, Colorado. This commentary outlines the main ideas and recommendations in this white paper, which are intended to strengthen the USIBWC's ability to respond to the challenges of U.S.-Mexico border water management in the 21st century. The paper recognizes the IBWC's long history of handling binational water issues effectively and its demonstrated capacity to respond and adapt to the border region's changing social, political, and environmental conditions. The commentary is capped with Commissioner Giner's response to the white paper, including her commitment to work with the academic community in both countries in creating an IBWC's binational science advisory group, as recommended in the white paper.