Groundwater is more than an aquifer map

In USGS's 2015 national accounting, groundwater provided about 39% of public-supply withdrawals and approximately 48% of irrigation withdrawals. Nearly all self-supplied domestic water came from groundwater. These are historical benchmarks, not current measurements; they show why groundwater matters well beyond the West.

A groundwater budget connects recharge, withdrawals, storage change, and discharge to streams, springs, and wetlands. Sustainable use depends on these exchanges and on acceptable impacts, not simply annual pumping equaling estimated recharge.

For a defined area and period, change in groundwater storage equals recharge plus net groundwater inflow and net surface-water exchange, minus pumping and groundwater evapotranspiration. Keep transfers and units consistent so river infiltration and irrigation returns are counted only once.

Well levels show local conditions; translating them into storage volumes requires aquifer properties and spatial coverage. Combine local observations with basin models and regional satellite context, and publish coverage gaps and uncertainty.

• Use repeated well-level measurements and pumping records to track trends.
• Monitor water quality alongside quantity, including domestic-well vulnerability.
• Assess stream baseflow, land subsidence, and the time needed for recharge to reach usable storage.

Additional rainfall is not automatically recoverable groundwater. Recharge projects need suitable geology, available water, acceptable water quality, and monitoring that distinguishes infiltration from dependable supply. Set basin-specific thresholds and revise pumping and recharge operations as evidence changes.