The duty to cooperate is a universal principle engrained in International Law. A sequel to this principle is the concept of equitable participation and taking all appropriate measures not to cause significant harm. These principal norms in International Water Law can only function through the cooperation of states. Bilateral and multilateral treaties make this duty a mandatory obligation for contracting parties. Nevertheless, disputes still exist among riparian states over their use of international shared waters. This paper, therefore, seeks to determine how the application of the duty to cooperate in the development of transboundary water can be achieved through the procedural norm of equitable participation and the substantive norm of taking all appropriate measures not to cause significant harm. Through a doctrinal (analytical) approach, empirical studies, as well as the legal framework on international watercourses management will be examined to understand the various roles of states on a transboundary river. The duty to cooperate will also be appraised to ascertain the modalities for its application in International Water Law. This study aims to foster a sustainable pathway to ensuring cooperation in the use of international waters in state interactions. This is relevant for equitable utilization of the waters and their resources.