When a state claims its practices are lawful but at the same time another claims this unlawful, a paradox emerges. Legal indeterminacy becomes the ordinary rule, while the resolution of disputes is designated the exception. To illustrate how international law deals with paradoxes, this paper will employ the dichotomy of upstream–downstream trans-boundary interstate relations. Here the paradox arises, since upstream states traditionally advocate for the free utilisation of water within their territory, while downstream states instead advocate for the waters full continued flow. Although, from a logical perspective, such a paradox would typically be viewed as something negative, from a social perspective, paradoxes also draw attention to the frames of common sense. Indeed, by employing a Luhmannian-inspired theoretical framework, this paper proposes that, through a sociological understanding of paradoxes, one can more adequately rediscover and reconceptualise the manner in which international law institutionalises conflicting expectations into a more harmless, bounded and permitted contradiction.