The relevance of the main instruments of international water law to the hydraulic development projects of later-developing upstream states is explored, for a non-legal audience. Relevance is gauged by querying common misperceptions, checking the compatibility of the instruments, and considering their effect along the Nile, Jordan and Tigris Rivers and associated aquifers. Specific principles of international water law are found to support upstream development in theory, though its relevance is threatened by incompatibility of clauses between the instruments, the erosion of normbuilding processes, and a shift away from the idea that territorial sovereignty over a fluid resource should be limited. 2 The question arises in the non-legal water community: Should we care enough about this progress to learn the language and issues, and engage in the debates?Certainly water resource managers, diplomats and researchers should, for tensions between upstream and downstream states are increasing, and a compelling case has been made that IWL favours those downstream nations that have already developed the transboundary resource (Wegerich & Olsson, 2010). This article queries that argument by investigating the extent to which IWL is relevant to the later-developing, upstream states. It follows a tradition of articles on water law in Water International (e.g. Leb, 2015;Vink, 2014;Wouters & Chen, 2015), though in considering also the politics of water interaction between states, it is written for a non-legal water audience. The relevance is gauged by reviewing common misperceptions about law and lesser-known clauses, then by cross-checking the mutual compatibility of the many legal instruments that make up the body of IWL, and finally by querying the effect of IWL on the behaviour *Email: m.zeitoun@uea.ac.uk 2 of riparian states along the Jordan, Nile, and Tigris Rivers and associated aquifers. This is preceded by a critical review of the relevant legal principles and debates, and followed by discussion of the implications of the findings.The analysis finds that on the whole, IWL is entirely relevant to all late-developing upstream states. Taken (momentarily) out of the political context, the chief legal instruments are found to contain no provisions which compromise upstream development or privilege downstream development. This theoretical relevance of IWL is found to be threatened, however, through a perceptible shift away from coordinated to unilateral transboundary activity, through erosion of the norm-building feature of international law (as when IWL is ignored or discredited by those seeking to maintain the status quo) and through incompatible clauses (in particular the sovereignty clause in the Draft Aquifer Articles). IWL's actual influence over the transboundary water arrangements in the cases considered is found to be qualified, revealing how the threats may and do play out in practice. The article argues that the advances IWL has made in tackling the collective challenge of governing a fluid transboundary resource a...