Sustainable yield is the amount of water that can be withdrawn from a water source (aquifer, reservoir, or basin) over the long term without causing unacceptable environmental, economic, or social consequences.
Sustainable yield defines the maximum rate at which water can be extracted from a source on an ongoing basis without depleting the resource, degrading water quality, or causing unacceptable impacts on dependent ecosystems, other water users, or the resource itself. For groundwater, sustainable yield has evolved from the earlier concept of safe yield (which equated it to natural recharge) to a more comprehensive concept that accounts for the effects of pumping on streamflow, wetlands, springs, land subsidence, saltwater intrusion, and water quality. The sustainable yield of an aquifer is typically less than its natural recharge rate because some portion of recharge must be preserved to maintain baseflow in rivers, support groundwater-dependent ecosystems, and prevent compaction of aquifer materials. For surface water systems, sustainable yield considers hydrologic variability, reservoir operations, downstream flow requirements, and the reliability needed by different user sectors. Determining sustainable yield requires long-term hydrologic data, understanding of system dynamics, and value judgments about acceptable levels of risk and environmental impact. Many aquifers and river basins worldwide are currently being exploited beyond their sustainable yield, resulting in declining water tables, reduced streamflow, land subsidence, and water quality degradation. Adaptive management approaches that adjust extraction rates based on monitoring data are increasingly recognized as essential for achieving truly sustainable water use.