The main purpose of this legislation is to reauthorize and update the United States-Mexico Transboundary Aquifer Assessment Program. This program is designed to assess and manage shared aquifers that cross the border between the United States and Mexico, ensuring sustainable water resources for both countries. Key provisions of the legislation include the expansion of the areas covered by the assessment program. Specifically, it adds Arizona to the list of states that can participate in the program, while also excluding certain aquifers that are already designated under existing state orders.