Groundwater is water located beneath the earth's surface in soil pore spaces and in the fractures of rock formations. Groundwater is recharged from, and eventually flows to, the surface naturally. Natural discharge often occurs at springs and seeps, and can form oases or wetlands. It can also be mechanically withdrawn for agricultural, municipal and industrial use by constructing and operating extraction wells.
Groundwater is a significant source of water supply that provides over 35% of Southern California's drinking water. Effective use of local groundwater basins is an important component of the region's water supply plan. Although Metropolitan does not own or control groundwater basins in Southern California, it has played a critical role as the region's supplemental water supplier in helping replenish the basins as well as being involved in groundwater recovery projects that treat groundwater with impaired water quality.
Metropolitan sponsors various groundwater storage programs, including, cyclic storage programs, long-term replenishment storage programs, and contractual conjunctive use programs. Conjunctive use refers to the practice of storing imported surface water in groundwater basins during years when there is a surplus of supply for use in times of drought or other supply interruptions.
Groundwater Assessment Study
In 2007, Metropolitan prepared the Groundwater Assessment Study in collaboration with its member agencies and with groundwater basin managers. This study evaluated the potential for groundwater storage and identified the challenges in developing additional storage programs within Southern California.
In addition to regional groundwater programs, Metropolitan collaborates with other water agencies throughout the state on water transfer and storage projects that often includes groundwater storage or "banking" programs.
Regional Progress Report: Achievements in Conservation, Recycling and Groundwater Recharge.