HydroConnect focuses on the connectivities afforded by hidden, underground fresh water that surfaces along the coastlines of islands lacking accessible, perennial fresh water. It explores how Austronesian-speaking seafarers transformed such freshwater ‘seeps’ into wells throughout the South China Sea and Indo-Pacific, affording sea-routes around these well networks. Thus, HydroConnect breaks with the tendency in the social sciences and historiography to analytically privilege oceans or navigable rivers as vectors of global connections and history-making. With the innovative concept of hydroconnectivities – human connections afforded by fresh water access – HydroConnect develops a novel theoretical framework linking the terrestrial and the aquatic through comparative historical ethnography of Austronesian speakers’ Indigenous knowledge, which has crossed oceans and flowed down generations, travelling between different groups of people. Deploying a cyclical tidalectic methodology transcending anthropology, archaeology and geology, it breaks new methodological and theoretical ground for conceptualising global history through hydrological connectivities across these chains of island worlds in different oceans. First, it studies how this travelling Indigenous knowledge enabled hydroconnectivities that opened up sea routes and integrated fresh water, well infrastructure, and ecological and social exchanges across immense oceanic spaces in the past. Second, the project maps and theorizes how present-day descendants and successors of Austronesian-speaking seafarers benefit from vernacular hydrological knowledge of underground freshwater seeps. Thus, it advances analogical knowledge for tackling groundwater depletion to enable past-informed and future-oriented water policies for the sustainable management of the Earth’s aquifers.