Statewide, groundwater provides about 30 percent of California’s water supply, with some regions more dependent on it than others. In drier years, groundwater provides a higher percentage of the water supply. Groundwater is less known than surface water but no less important. Its potential for helping to meet the state’s growing water demand has spurred greater attention toward gaining a better understanding of its overall value. This issue of Western Water examines groundwater storage and its increasing importance in California’s future water policy.