The issue of transboundary harm has been a matter of concern, especially in disasters like Chernobyl or the Sandoz Oil Spill. In both these incidents, the absence of any jurisprudence at the global level on the notion of ‘transboundary harm’ created multiple challenges in assessing liability. These two incidents have become prime examples of the difficulties created by the idea of absolute territorial sovereignty in international law. The International Court of Justice (ICJ) has brought considerable momentum to address this gap in the past few decades with the Corfu Channel case (1949) and Threat or Use of Nuclear Weapons in the context of the use of force and towards a wider ambit of transboundary harm in the Gabcikovo-Nagymaros case (1997) specifically for transboundary water sharing. The Pulp Mills Case and Costa Rica v. Nicaragua (2006) have pushed the jurisprudence towards expanding the purview of transboundary harm to include Environment Impact Assessment (EIAs) as a part of due diligence within its framework. The paper examines the transition facilitated by the ICJ in the jurisprudence on transboundary harm and its potential impact on transboundary water governance in South Asia. It also explores opportunities and gaps by looking at some South Asian agreements on water sharing in the context of legal principles on transboundary harm in international law.