The lack of a settled definition for hydropolitics—a prismatic concept that acquires specific meanings according to both the disciplinary boundaries within which it is used and the theoretical perspectives of those employing it—is consistent with the disagreement over its nomenclature (hydro-politics vs. hydropolitics). The term has had many meanings and idiosyncratic usages over time, and there has been hardly any attempt to advance a clear definition for it. The strength of the concept of hydropolitics, its inter-disciplinary conceptual heterogeneity, is also its weakness. While the crystallization of some of the core features of hydropolitics in the literature—especially with regard to scale (namely, the focus on the inter-state level and the range of issues covered, that is, the politics of international water basins)—has anchored hydropolitics to “standard cases” of the concept, its theoretical underpinnings are still blurred. The study of hydropolitics has substantially delved into trans-boundary, not just any, waters. Yet, both the ontology and epistemology of the concept are debatable, so few eclectic definitions for hydropolitics have emerged. Hence, by addressing the relationships between knowledge, theory, and action of hydropolitics, the scientific community, in particular scholars of international relations, political geography, and critical geopolitics, has struggled for theoretical coherence as well as for conceptual clarity over the use of the term. This is not an easy task, though, because the fluid essence of hydropolitics escapes not only definition but also easy classification.