The paper advances scholarship on water appropriation by examining the appropriation process at the metropolitan scale, foregrounding inequities in intra-metropolitan water distribution, and applying the lens of technopolitics to deepen insight into the processes underpinning water appropriation. It illustrates how water is legitimately appropriated for the city of Mumbai, depriving other municipal corporations, councils, and industrial centres within the metropolitan region. The paper demonstrates how technical decisions—such as adopting a river basin development approach and framing the diversion of water originally reserved for irrigation to Mumbai as a temporary and emergency measure—were strategically employed to legitimise appropriation as a natural, depoliticised process. The river basin approach, typically perceived as promoting integrated planning, was used to carve out the Mumbai Hydrometric Area (MHA), following hydrological boundaries to gain control over water resources on the mainland. Meanwhile, framing water diversion as a technical and emergency measure assisted in avoiding potential criticism from farmers and civil society. The sense of urgency was crafted by overestimating water demand and exaggerating short-term water shortages, thereby limiting the scope for long-term solutions and presenting diversion as the only viable technical option. Through these technopolitical manoeuvres, Mumbai, geographically located on an island, legitimately secured control and selectively appropriated suitable water resources on the mainland.