California’s Department of Water Resources has released its most comprehensive groundwater report to date. The Bulletin 118 Update 2025 covers groundwater conditions, use, and management across the state from 2020 to 2024, offering the most detailed assessment yet of a resource that supplies around 40% of California’s total water demand in average years.
Drawing on data from nearly 9,000 monitored wells, satellite-based subsidence mapping, and the first full decade of reporting under the Sustainable Groundwater Management Act (SGMA), it covers a period marked by record-setting drought, historic atmospheric rivers, and accelerating climate stress, presenting the clearest picture yet of a resource that is both indispensable and increasingly strained.
The report amounts to a call for California to move from reactive groundwater management to treating it as the cornerstone of its long-term water strategy
Structured around four strategic themes: maximizing groundwater infrastructure for climate adaptation, accelerating SGMA implementation, strengthening equity for frontline communities, and improving data and monitoring tools, the report amounts to a call for California to move from reactive groundwater management to treating it as the cornerstone of its long-term water strategy. We highlight some key aspects emerging from the report: the sheer scale of what lies underground, a landmark policy shift in how aquifers are classified, and a promising operational strategy for turning flood events into long-term storage.
A legislative turning point
California’s total groundwater storage capacity exceeds 1,000 million acre-feet, approximately 25 times the combined storage of all the state’s surface reservoirs. During droughts, groundwater’s contribution to total state water demand can rise to nearly 60%. Yet for much of its history it has been managed reactively, drawn down heavily in dry years and given little structured attention in wet ones.
During droughts, groundwater’s contribution to total state water demand can rise to nearly 60%
A key milestone came in 2023, when Senate Bill 122 formally designated aquifers as natural infrastructure, placing them alongside roads, levees, and canals as assets requiring active investment and protection. It unlocks new categories of public funding for recharge projects and storage enhancement, reframing the policy conversation: aquifers are not a backup supply but a foundational component of the state’s water system to be actively managed across the full hydrologic cycle.
DWR Director Karla Nemeth framed the opportunity directly in the report: “Beneath our feet lies not only a vast reservoir, but also a powerful opportunity to rethink how we connect land, water, infrastructure, and climate resilience in a changing world.”
Turning floods into storage
One of the most operationally significant shifts documented in the update is the growing role of Flood-MAR, flood-managed aquifer recharge, as a deliberate management strategy rather than an opportunistic afterthought.
In 2023, following a record-breaking sequence of atmospheric rivers, California achieved approximately 4.9 million acre-feet of managed aquifer recharge statewide in a single year, more than 40% of the sustainable annual yield of the state’s highest priority basins, with 83% occurring in the San Joaquin Valley, precisely where overdraft is most severe. Emerging tools such as forecast-informed reservoir operations for managed aquifer recharge (FIRO-MAR) aim to systematize this approach, using improved precipitation forecasting to route water to high-priority recharge zones before it becomes a flood management problem.
From opportunistic to strategic
The report calls for aquifer recharge potential mapping across the state, expansion of real-time monitoring networks, and tighter integration between surface water operations, flood management, and groundwater sustainability programs. A statewide 10-year comparison shows groundwater levels rose five feet or more in 41% of monitored wells between 2014 and 2024, the first time increases have outpaced declines in such a comparison. But cumulative deficits remain significant in critically overdrafted basins, and climate projections point to growing demand on a resource already under stress.
The message from the 2025 update is clear: California’s groundwater is too large, too critical, and too vulnerable to continue managing as an afterthought.