Through analysis of North American water treaties, this article specifies criteria for determining the quasi-constitutionality of freshwater treaties in order to determine if some of them have quasi-constitutional standing. These criteria, temporal, substantive, and contextual, are applied to treaties found in the Transboundary Freshwater Dispute Database at Oregon State University (TFDD). Of 74 agreements (with 50 years standard duration), only six agreements meet or come close to meeting the quasi-constitutional standard, not counting the North American treaties. We conclude that while quasi-constitutional treaties are rare among the more than 600 in the TFDD, they reinforce international water law and strengthen social cohesion among the contracting states. They also highlight the importance of both substantive and contextual conditions in consolidating support for such treaties.