Throughout the world, international and state political boundaries divide ground water resources into politically convenient jurisdictions. Subsurface water, however, does not recognize such borders and flows freely without regard to overlying politics. This disregard for the political dimension, coupled with the growing global importance of fresh water, has the potential for aggravating disputes and conflicts over the use, allocation, and preservation of such resources. To date, widely accepted norms of international law applicable to transboundary aquifers have yet to emerge. However, local and regional agreements, including both formal and unofficial arrangements, suggest the emergence of state practice that should be considered as bases for emerging customary international law.This paper reviews transboundary ground water agreements in North America at both the subnational and international levels. These range from informal memoranda of understanding between bordering sister cities, to formal international agreements involving nations. Significantly, the majority of the arrangements identified are unofficial pacts without formal endorsement of the respective governments, and most were concluded at the subnational level. Although the agreements and their scope vary dramatically, many commonalities do exist. These include an emphasis on generally accepted international principles of cooperation, prior notification of planed activities, sharing of data and information, and public participation. They also underscore a preference for subsidiarity and for developing local solutions for local issues.In addition to identifying these commonalities, this paper reviews the legal mechanisms employed by the parties in an effort to better appreciate drafting and enforcement concerns. Furthermore, dissimilarities related to differences in geology, climate, local needs, and other unique factors are addressed. Finally, the paper considers the changing function of regional agreements and their role in the development of international custom, and concludes by emphasizing the importance and effectiveness of local and regional agreements that are tailored to local characteristics and circumstances
