New groundwater agencies in the Sacramento Valley are currently finalizing plans to manage their groundwater basins for long-term balance, as required by the Sustainable Groundwater Management Act (SGMA). Successful stewardship demands good information not only about groundwater conditions, but also about surface water availability. To help build shared understanding of surface water for agriculture—the valley’s main water-using sector—we produced a new dataset showing how access to this vital resource varies across irrigated farmland in the Sacramento Valley and the Delta.