The Pacific archipelago of Vanuatu faces a unique set of challenges due to its exposure to natural hazards, including earthquakes, cyclones, volcanic eruptions, and tsunamis. Coupled with the impacts of climate change, such as rising sea levels and coastal erosion, the region's freshwater resources face increasing scarcity and accessibility issues. The limited hydrogeological knowledge in Vanuatu restricts access to drinking water and hinders local development. In this context, an 18-day scientific expedition was conducted in 2023 to improve hydrogeological understanding and empower local stakeholders through targeted training initiatives in hydrogeology and isotope geochemistry. Extensive sampling for precipitation, surface waters and groundwater was conducted on Ambae and Tanna, two islands with distinct hydrogeological contexts. In situ measurement of physico-chemical parameters and water sampling for major ions, isotopic analysis and trace metals was performed. Sampling of rain water reservoirs allowed to define a local meteoritic water line. An isotope-altitudinal gradient in precipitations helped to constrain the recharge altitudes of groundwater resources used for drinking water (sources and wells). Major ions analysis indicates freshwater-seawater mixing, highlighting groundwater resource vulnerability to climate change. All field work was planned and conducted in close collaboration with Vanuatu’s Department of Water Resources, promoting capacity-building initiatives for hydrological assessments. The collaborative efforts not only advanced scientific knowledge but also empowered local communities to take proactive measures in managing water resources sustainably. The outcomes of this program provide valuable insights for addressing the complex water challenges faced by Vanuatu, paving the way towards a more resilient and water-secure future.