Nepal and India share deep geographical ties, with many Indian rivers originating in Nepal’s mountainous catchments. Beyond major systems like the Kosi and Gandak, about 6000 rivers flow from Nepal into India. While large rivers receive significant attention, smaller transboundary rivers present notable water-related challenges, particularly in Bihar’s border areas adjoining Nepal’s Terai. A major risk from these smaller rivers is flash flooding, causing severe, localized damage. Bihar districts like Pashchim Champaran, Purbi Champaran, Sitamarhi, Madhubani, Supaul, Araria, and Kishanganj frequently face such floods triggered by pahadi (hilly) rivers. Another shared concern is arsenic contamination in groundwater, found in Terai aquifers. This poses a serious health risk, as rural communities on both sides of the border depend heavily on groundwater for drinking. These dual challenges, flash floods and groundwater contamination, underscore the urgent need for a joint governance framework to manage water-related risks. Such a model could serve as a blueprint for addressing similar issues along other stretches of the Nepal-India border. This paper attempts to illustrate these using examples from the border areas in Bihar with the Terai of Nepal.