Groundwater replenishment happens through direct recharge and in-lieu recharge. Water used for direct recharge most often comes from flood flows, water conservation, recycled water, desalination and water transfers, according to DWR.
During the hydrologic cycle, replenishment occurs naturally when rain, stormwater, and the flow from rivers, streams and creeks seeps into an aquifer. Water also gets into ground as farmers irrigate fields and orchards. Replenishment within the context of groundwater management is accomplished through recharge at rate that exceeds baseline conditions, maintaining or improving groundwater elevation levels. Two recharge methods are used: direct spreading and aquifer injection.
There is also in-lieu recharge in which an alternative source is provided to users who would normally use groundwater, thereby leaving groundwater in place for later use and increasing the potential to improve groundwater levels. According to DWR, institutional and regulatory issues, spatial and temporal connectivity of the water system, data availability, water quality, system operations and capacity, financial feasibility, and environmental sustainability are barriers to expanded recharge activities.