Global food systems rely on irrigated agriculture, and most of these systems in turn depend on fresh sources of groundwater. In this study, we demonstrate that groundwater development, even without overdraft, can transform a fresh, open basin into an evaporation dominated, closed-basin system, such that most of the groundwater, rather than exiting via stream baseflow and lateral subsurface flow, exits predominantly by evapotranspiration from irrigated lands. In these newly closed hydrologic basins, just as in other closed basins, groundwater salinization is inevitable because dissolved solids cannot escape, and the basin is effectively converted into a salt sink. We first provide a conceptual model of this process, called “Anthropogenic Basin Closure and groundwater SALinization” (ABCSAL). Next, we introduce a mixing cell solute transport model to calculate the timescales under which salinization threatens groundwater quality in California's Tulare Lake Basin, and compute the water and salt budgets across these timescales. Results indicate that under modern water management practices in the Tulare Lake Basin, shallow aquifers (48 m deep) exceed maximum contaminant levels for total dissolved solids on decadal timescales. Intermediate (171 m) and deep aquifers (238 m), essential for drinking water and irrigated crops, are impacted within two to three centuries. Hence, ABCSAL resulting from groundwater development in agricultural regions worldwide constitutes a largely unrecognized constraint on groundwater sustainable yield, and poses a serious challenge to global groundwater quality sustainability, even where water levels are stable.