As surface water, such as rain, seeps into the ground, it passes between soil particles and collects in underground reservoirs called aquifers. An aquifer is made up of sand, silt, or other permeable materials that can readily yield water to springs or wells.
Groundwater is an essential part of the state and nationwide water supply. While San Francisco residents are not currently drinking groundwater, 80% of Californians depend on it for all or part of their drinking water supply, and have been doing so safely for generations.
Our Groundwater Program includes two projects, currently in progress, plus a stewardship and management program:
Together, these projects will increase our local and regional water supply reliability, diversify our water supply portfolio and reduce our dependence on a single source, making us less vulnerable to disrupted service from drought and natural disasters such as earthquakes.
Our future groundwater supply will come from the 45-square-mile Westside Basin, a series of aquifers extending from Golden Gate Park in San Francisco southward through San Bruno. The basin is a vital local resource for San Francisco and neighboring communities in San Mateo County.
In March, 2017, the San Francisco Public Utilities Commission (SFPUC) will start pumping groundwater from the Westside Groundwater Basin aquifer that extends to approximately 400 feet below the surface in San Francisco. The groundwater will be treated and blended with our regional drinking water supplies before it is delivered to our customers. Over the next few years we will continue adding groundwater in order to reach our goal of blending 4 million gallons a day (mgd) of treated groundwater with our regional water supplies by 2020.