Our Water System

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To understand the local supply challenges, it is important to know the three primary sources for Southern California's water and what's happening in those areas:

More than 60% of water used in the Central Basin service area comes from local groundwater. This is water stored in groundwater basins, filled by rainwater that has percolated down and also by water used for irrigation. This year, these local supplies were impacted by the statewide drought, which brought record-low rainfall of 3.21 inches of rain, a major decrease from the annual average of 14 inches of rain recorded in Southern California in previous years.

The remaining 40% of Central Basin's water is imported from the Colorado River and Northern California through the State Water Project.

The State Water Project (SWP), which draws its water from California's Sierra snow pack, provides water for more than 23 million Californians. Melted snow flows down from the Sierras into the SWP, where it is stored behind the Oroville Dam and gets released throughout the year down the Sacramento River through the "Delta," where it finally reaches Southern California via the California Aqueduct system. This past year, low Sierra snow pack levels - recorded at only 85% of normal - reduced available water supplies to the SWP.

Environmental concerns have also affected the SWP this year. In the summer, a small fish called the Delta Smelt was found to be endangered by the pumps that push the water to Southern California. This environmental disruption has resulted in a federal court order to shut down the pumps at certain times. This could result in Southern California losing as much as 30% of its annual supply from SWP.

At the Colorado River, nearly a decade of drought conditions has critically impacted two of California's largest reservoirs - Lake Mead and Lake Powell - which store water supplied by the Colorado River. For the past seven years the water level of each lake, which is currently at a staggering 50%, has continued to decline.

These are a few of the key issues impacting Southern California's water supply. At Central Basin, we understand that managing these issues is no easy task, but with planning, partnerships, strategic conservation efforts and your support, we can survive the drought.

Read MWD's Press Release on the Delta Smelt Ruling Here.