Water is crucial for meeting sustainability targets, but its unsustainable use threatens human wellbeing and the environment. Past assessments of water scarcity (i.e., water demand in exceedance of availability) have often been spatially coarse and temporally limited, reducing their utility for targeting interventions. Here we perform a detailed monthly sub-basin assessment of the evolution of blue (i.e., surface and ground) water scarcity (years 1980-2015) for the world’s three most populous countries – China, India, and the USA. … Our work also demonstrates that efforts to improve water sustainability in the study countries have largely fallen short of reversing these undesirable trends and that large-scale coordinated interventions are urgently needed in order to realize substantial positive change and to meet water sustainability targets. Close evaluation of the success of several more recent efforts in the studied countries (e.g., California’s Sustainable Groundwater Management Act (2014) …