California has two gigantic water development systems which capture and store water with many dams and use rivers and canals to redistribute it, generally from Northern California sources (or "areas of origins") to the San Joaquin Valley agricultural users and southern California cities—same as today. They are:

• California State Water Project.
• Federal Central Valley Project.

These water projects have low priority water rights, which were acquired starting only in the 1920s and 1930s. Their rights are considered "junior" to more "senior" rights held by many irrigation and water districts in the Central Valley as well as rights held by the City and County of San Francisco, Pacific Gas & Electric Company, Southern California Edison Corporation, and East Bay Municipal Utilities District (which supplies Mokelumne River water to Alameda and Contra Costa counties).

The Central Valley Project

Originally conceived by state engineers, the US Bureau of Reclamation took over construction of the Central Valley Project. The Bureau claims this profile of the project:

• Reaches from the Cascade Mountains near Redding in the north some 500 miles to the Tehachapi Mountains near Bakersfield in the south.
• Is comprised of 20 dams and reservoirs, 11 powerplants, and 500 miles of major canal as well as conduits, tunnels, and related facilities. 
• Annually delivers about 7 million acre-feet for agriculture, urban, and wildlife use.  
• Provides about 5 million acre-feet for farms -- enough to irrigate about 3 million acres or approximately one-third of the agricultural land in California. 
• Furnishes about 600,000 acre-feet for municipal and industrial use, enough to supply close to 1 million households with their water needs each year. 
• Dedicates 800,000 acre-feet per year to fish and wildlife and their habitat and 410,00 acre-feet to State and Federal wildlife refuges and wetlands pursuant to the Central Valley Project Improvement Act (CVPIA).  
• During an average water year, generates about 4.8 billion kilowatt hours of electricity to meet the needs of some 2 million people.

Water Rights Primer

The State Water Project

The California State Water Project was approved by the legislature in 1959 and bonds for its construction narrowly approved by California voters in November 1960 (Proposition 1). The California Department of Water Resources claims this profile for the State Water Project:

The Department of Water Resources still claims the overall "entitlements" of the State Water Project contractors total 4.23 million acre-feet per year. The project has never in its history delivered that much water, and has delivered no more than about 2.6 million acre-feet in its largest year. Controversy over the project's capacity during droughts led to adoption of the secretly negotiated "Monterey Agreement" in 1994 and project contract amendments in 1995.

Water Rights Primer