Data and information exchange are vital for long-term transboundary water cooperation. However, many transboundary river basins lack regular data exchange between riparian States. In many cases, this is simply a feature of the generally fragmented nature of transboundary water cooperation; in others, transboundary river basin data sharing may be withheld for geopolitical reasons. The Tigris-Euphrates and Indus river basins are among the most highly politicized river basins globally. Cooperation between riparians is complicated by a lack of certainty regarding data, information exchange and legal obligations, as upper riparians in both basins have persistently objected to the customary law of international watercourses. With reference to international water law, this article ascertains the level of data and information exchange in these two basins, both through formal and informal structures, as well as prevalent obstacles and the institutional and technological responses to them. Despite significant challenges, the authors argue that technological advances can stimulate enhanced riparian cooperation.