Where Does California Get its Water

Even as the available supply of water dwindles in California, the state’s increasing demand from population and drought means water suppliers and water users must do all they can to squeeze the most use from each precious drop of water. Where Does California Get its Water?

Where Does California Get its Water?

California’s H2O supply comes from 2 main sources:
Surface-H2O that travels or gathers on the ground, like rivers, streams, & lakes
Groundwater-H2O that’s pumped from the ground

Watersheds North of Sacramento-75% from rain & snow
Drainage Basins in Central Valley-20%
Colorado River


The state of California moving into the 20th century decided to build thousands of miles of a complicated web of water reservoirs, dams, pipelines, aqueducts, and canals to ensure water to the lower southern end of the growing populated cities of the state.



Where Does Northern California Get its Water


How Water Gets From the Sierra Nevada Mountains to the Rest of California – NBC Los Angeles
Northern Aqueducts

 Northern California’s main supply of water around 75% where only 20% of California’s population resides comes from surface water and is replenished by precipitation in the form of rain or snow that melts in the spring. This is because most of the state’s precipitation occurs in the northern 1/3 of the state, above the city of Sacramento averaging 100 inches or more a year, where we find 75 percent of the available water. 

Westerly winds bring in moisture from the Pacific Ocean where they impact northern California’s high mountain ranges. The air rises mixes with colder air moving down from the Pacific Northwest and cools turning to precipitation.

Northwestern California sees 2x as much rain as London England gets in a year. This heavy precipitation moves south into the very northern parts of the Central Valley.

In order to move a supply of water from the wetter north to the drier south 2 main components were developed called Central Valley Project and the California State Water Project.

Using much-needed water for irrigation for farming in the Central Valley and for the growing population in cities like Los Angeles and San Diego inhabiting the southern end of the state. Reservoirs like Lake Shasta and Lake Oroville are seeing all-time lows but not to the levels seen in the Central and South.  


Where Does Central California Get its Water


Central Valley population 6.5 millio Area Km2 110,000 km2 Largest City ...Moving south is the Central Valley a vast agricultural region of California that covers about 20,000 square miles and is one of the more notable structural depressions in the world.

The Central area is bounded by the Cascade Range to the north, the Sierra Nevada to the east, the Tehachapi Mountains to the south, and the Coast Ranges with San Francisco Bay to the west.

The conveyance of water moving north to south relies on the movement of that water through the Delta and its maze of levees and islands while maintaining the right balance of saltwater and fresh water.

These mountain ranges surrounding the area North of Central Valley all have thick snow base in the winter that melts in the spring and summer months that fill California rivers and stream like the Sacramento and San Joaquin rivers providing much-needed water. They supply water to the Sacramento-San Joaquin Delta, a water source that serves roughly 25 million Californians via the State Water Project.

The northern one-third is known as the Sacramento Valley and the southern two-thirds is known as the San Joaquin Valley. About 75% of the irrigated land in California and 17% of the Nation’s irrigated land is in the California Central Valley. About 20% of the state’s groundwater demand is supplied from pumping Central Valley aquifers, making it the second-most-pumped aquifer system in the U.S. 

The Sacramento-San Joaquin Delta is the hub of California’s water supply, supplying fresh water to two-thirds of the state’s population and millions of acres of farmland. Saltwater from the San Francisco Bay mixes with fresh water from the Sacramento, San Joaquin, and other rivers to create the largest estuary on the West Coast. Groundwater accounts for about 30% of the annual supply of both types of water used for agricultural and urban purposes.


Where Does Southern California Get its Water


Moving south of the Central Valley lies the Southern region of California which holds 80% of the population but only produces around 20% of the state’s supply of water. This means that a large portion of water that is produced in the Northern end of California is pumped down into the dry arid regions of southern California to meet their much larger demand.

Here lies the most critical problem that contributes to the California water crisis. Around 200 million acre/ft. of water will fall on California annually from rain snow and water imported elsewhere.

  • Half of this amount is consumed by nature in evaporation or drains into the Pacific Ocean.
  • Half is consumed by humans and agriculture or 100 million acres. 

An acre-foot of water equals about 326,000 gallons or enough water to cover an acre of land which is (the size of a football field 1 foot deep). An acre-foot of water is a common way to measure water volume and use especially in the western part of the US where water is measured daily.

Unfortunately, these numbers fluctuate to up to 40% and are dependent on variables like wet months between December and February in the northern end, snow melt in Sierras Nevadas, and the Cascades mountains and what scientists call the Mega Drought in the country’s southwest. The drought lasting now 22 years has put tremendous stress on all sources of water feeding numerous states in the southwest region of the US.


Does California Get Water From the Colorado River


Yes, via the Colorado River Aqueduct is a 242 mi water conveyance in Southern California in the United States, operated by the Metropolitan Water District of Southern California (MWD). The aqueduct takes water from the Colorado River at Lake Havasu on the California-Arizona border, west across the Mojave and Colorado deserts to the east side of the Santa Ana Mountains. It is one of the primary sources of drinking water for Southern California.

The Metropolitan Water District of Southern California is the largest supplier of treated water in the United States.  It is a cooperative between fourteen cities, eleven municipal water districts, and one county water authority, providing water to 19 million people in a 5,200-square-mile service area. It was created by an act of the California Legislature in 1928, primarily to build and operate the Colorado River Aqueduct.



Will California run out of Water?

Yes, California will run out of water within 1 year, says, Jay Famiglietti, a NASA senior Water Scientist at the Jet Propulsion Laboratory. Data reveals that total H2O storage in Ca. has been declining since 2002 when satellite-based monitoring began, & groundwater depleting since the early 20th ……………………………………………………………. Read more

Who Uses the Most Water Supply in California

Water in California is shared across three main sectors. Statewide, average water use is roughly 50% environmental, 40% agricultural, and 10% urban, although the percentage of water use by areas changes dramatically across regions and between wet and dry years.

Water that is used for environmental causes falls into four categories:

  • river water is protected as “wild and scenic” under federal and state laws
  • water is required for maintaining habitat within streams
  • water that supports wetlands within wildlife preserves
  • water needed to maintain water quality for agricultural and urban use

California State Water Sources Map


California regions and water resources.California’s dependency is based on two sources of its water: surface water and groundwater. It’s so important that California monitors groundwater and surface water throughout the state.

The water that runs into rivers, lakes, and reservoirs is called “surface water.” Groundwater is found beneath the earth’s surface in the pores and spaces between rocks and soil. These are called aquifers. Groundwater supplies and wells are collected and water quality is monitored by the state.

Most of California’s precipitation falls as snow in the northern part of the state in the watersheds north of Sacramento during the winter. The snow acts as a natural reservoir, storing water until the spring runoff. After initial evaporation, percolation into the ground, and transpiration 

the water flows into streams and rivers and makes its way toward the ocean or down into salt sinks. Their water is counted as natural underground  Aquifers on a current water source database for the state of California and is measured as Groundwater is monitored on a state-live interactive site.

The South Bay Aqueduct is an aqueduct located in the eastern part of the San Francisco Bay Area. It conveys water from the Sacramento-San Joaquin Delta through over forty miles of pipelines and canals. It is overseen by the state of California Regional Water Management.


See the source image


The aqueduct flows along the eastern and southern edges of the Livermore Valley. Then it flows through a series of tunnels to an end in the foothills of eastern San Jose, 5 miles from downtown San Jose, California.

Meets Southern California and the Colorado Aqueduct that’s supplied from the Colorado River which can be thought of as a man-made river is capable of transporting up to 1 billion gallons of water daily to Southern California’s urban regions, according to the Bureau of Reclamation. 


What Type of Water Rights are in California?

In California, water rights are based on a hybrid mixture of riparian & appropriative rights issued & managed by the state & federal government to benefit all Californians giving individuals & others the right to beneficially use underground & surface water subject to seasonal & drought ……………………………………………………………………… Read more



JimGalloway Author/Editor



USGSCalifornia Central Valley

California Dept. of Water Resources- The Delta


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