The South Asian region comprising countries namely India, Pakistan, Afghanistan, Nepal, Bhutan, Sri Lanka, Bangladesh, and Maldives, holds a significant geo-political and economic position. These countries share a complex history of colonialism which led to a political demarcation of boundaries resulting in various problems in sharing common sources/water bodies in the region. This paper focuses on the historical development of hydro diplomacy in South Asia, with an emphasis on the Indus River Basin, Kabul River Basin & GangaBrahmaputra-Meghna River Basin in an attempt to scrutinize water politics in South Asia. A substantial number of bilateral agreements and treaties have been signed amid different countries of the region to ensure the maximum utilization of its vast river systems. However, challenges remain in managing water resources at a regional level effectively and addressing the needs of all stakeholders. Understanding the historical development of hydro diplomacy provides insights into the complexities faced in managing transboundary water resources in South Asia. This paper highlights the importance of cooperation, negotiation, and updated agreements to ensure sustainable and equitable use of water in the region in the backdrop of legal and customary International law on transboundary river water sharing.