Safe and just Earth System Boundaries (ESBs) for surface and groundwater (blue water) have been defined for sustainable water management in the Anthropocene. We evaluate where minimum human needs can be met within the surface water ESB and, where this is not possible, identify how much groundwater is required. 2.6 billion people live in catchments where groundwater is needed because they are already outside the surface water ESB or have insufficient surface water to meet human needs and the ESB. Approximately 1.4 billion people live in catchments where demand side transformations are required as they either exceed the surface water ESB or face a decline in groundwater recharge and cannot meet minimum needs within the ESB. A further 1.5 billion people live in catchments outside the ESB with insufficient surface water to meet needs, requiring both supply and demand-side transformations. These results highlight the challenges and opportunities of meeting even basic human access needs to water and protecting aquatic ecosystems.