Topic: Water Supply

Overview

Water Supply

California’s climate, characterized by warm, dry summers and mild winters, makes the state’s water supply unpredictable. For instance, runoff and precipitation in California can be quite variable. The northwestern part of the state can receive more than 140 inches per year while the inland deserts bordering Mexico can receive less than 4 inches.

By the Numbers:

  • Precipitation averages about 193 million acre-feet per year.
  • In a normal precipitation year, about half of the state’s available surface water – 35 million acre-feet – is collected in local, state and federal reservoirs.
  • California is home to more than 1,300 reservoirs.
  • About two-thirds of annual runoff evaporates, percolates into the ground or is absorbed by plants, leaving about 71 million acre-feet in average annual runoff.
Publication

Layperson’s Guide to Water Rights Law
Updated 2020

The 28-page Layperson’s Guide to Water Rights Law, recognized as the most thorough explanation of California water rights law available to non-lawyers, traces the authority for water flowing in a stream or reservoir, from a faucet or into an irrigation ditch through the complex web of California water rights.

Publication

Layperson’s Guide to the State Water Project
Updated 2013

The 24-page Layperson’s Guide to the State Water Project provides an overview of the California-funded and constructed State Water Project.

The State Water Project is best known for the 444-mile-long aqueduct that provides water from the Delta to San Joaquin Valley agriculture and southern California cities. The guide contains information about the project’s history and facilities.

Publication

Layperson’s Guide to Nevada Water
Published 2006

The 28-page Layperson’s Guide to Nevada Water provides an overview of the history of water development and use in Nevada. It includes sections on Nevada’s water rights laws, the history of the Truckee and Carson rivers, water supplies for the Las Vegas area, groundwater, water quality, environmental issues and today’s water supply challenges.

Publication

Layperson’s Guide to the Klamath River Basin
Published 2023

The Water Education Foundation’s second edition of the Layperson’s Guide to The Klamath River Basin is hot off the press and available for purchase.

Updated and redesigned, the easy-to-read overview covers the history of the region’s tribal, agricultural and environmental relationships with one of the West’s largest rivers — and a vast watershed that hosts one of the nation’s oldest and largest reclamation projects.

Publication

Layperson’s Guide to Integrated Regional Water Management
Published 2013

The 24-page Layperson’s Guide to Integrated Regional Water Management (IRWM) is an in-depth, easy-to-understand publication that provides background information on the principles of IRWM, its funding history and how it differs from the traditional water management approach.

Publication California Groundwater Map

Layperson’s Guide to Groundwater
Updated 2017

The 28-page Layperson’s Guide to Groundwater is an in-depth, easy-to-understand publication that provides background and perspective on groundwater. The guide explains what groundwater is – not an underground network of rivers and lakes! – and the history of its use in California.

Publication California Water Map

Layperson’s Guide to California Water
Updated 2021

The 24-page Layperson’s Guide to California Water provides an excellent overview of the history of water development and use in California. It includes sections on flood management; the state, federal and Colorado River delivery systems; Delta issues; water rights; environmental issues; water quality; and options for stretching the water supply such as water marketing and conjunctive use. New in this 10th edition of the guide is a section on the human need for water. 

Publication

Layperson’s Guide to the Central Valley Project
Updated 2021

The 24-page Layperson’s Guide to the Central Valley Project explores the history and development of the federal Central Valley Project (CVP), California’s largest surface water delivery system. In addition to the project’s history, the guide describes the various CVP facilities, CVP operations, the benefits the CVP brought to the state and the CVP Improvement Act (CVPIA).

Publication Sacramento-San Joaquin Delta Map

Layperson’s Guide to the Delta
Updated 2020

The 24-page Layperson’s Guide to the Delta explores the competing uses and demands on California’s Sacramento-San Joaquin Delta. Included in the guide are sections on the history of the Delta, its role in the state’s water system, and its many complex issues with sections on water quality, levees, salinity and agricultural drainage, fish and wildlife, and water distribution.

Maps & Posters California Water Bundle

California Water Map
Updated December 2016

A new look for our most popular product! And it’s the perfect gift for the water wonk in your life.

Our 24×36-inch California Water Map is widely known for being the definitive poster that shows the integral role water plays in the state. On this updated version, it is easier to see California’s natural waterways and man-made reservoirs and aqueducts – including federally, state and locally funded projects – the wild and scenic rivers system, and natural lakes. The map features beautiful photos of California’s natural environment, rivers, water projects, wildlife, and urban and agricultural uses and the text focuses on key issues: water supply, water use, water projects, the Delta, wild and scenic rivers and the Colorado River.

Aquapedia background California Water Map Layperson's Guide to California Water

Watershed

Sacramento River Basin

A watershed is the land area that drains snowmelt and rain into a network of lakes, streams, rivers and other waterways. It typically is identified by the largest draining watercourse within the system. In California, for example, the Sacramento River Basin is the state’s largest watershed.

Aquapedia background California Water Map Layperson's Guide to California Water

Water Supply in California

SnowmeltCalifornia’s “Mediterranean” climate, characterized by warm, dry summers and mild winters, is considered one of its great attractions, but it also can be unpredictable with flooding followed by drought and few years of “normal” precipitation.  [See also Hydrologic Cycle].

Aquapedia background California Water Map Layperson's Guide to California Water

Sierra Nevada

The Sierra NevadaStretching 450 miles long and up to 50 miles wide, the Sierra Nevada makes up more than a quarter of California’s land area and forms its largest watersheds, providing more than half of the state’s developed water supply to residents, agriculture and other businesses.*

San Luis Reservoir

Aerial view of San Luis Reservoir

The San Luis Reservoir is the nation’s largest off-stream reservoir, serving as a key water facility for both the State Water Project (SWP) and the federal Central Valley Project (CVP).

Aquapedia background California Water Map California Water Map, Spanish

Los Angeles Aqueduct and Owens Valley

Los Angeles Aqueduct Cascades The Owens Valley in eastern California helped transform distant Los Angeles into today’s sprawling megalopolis.

More than 100 years ago, Los Angeles recognized the need to augment local water supplies and decided to tap faraway sources.

Aquapedia background Colorado River Basin Map

Lake Powell and Glen Canyon Dam

Image shows Glen Canyon Dam with Lake Powell in the background.The construction of Glen Canyon Dam in 1964 created Lake Powell. Both are located in north-central Arizona near the Utah border. Lake Powell acts as a holding tank for outflow from the Colorado River Upper Basin States: Colorado, New Mexico, Utah and Wyoming.

The water stored in Lake Powell is used for recreation, power generation and delivering water to the Lower Basin states of California, Arizona, and Nevada. 

Dams

Folsom Dam on the American River east of Sacramento

Dams have allowed Californians and others across the West to harness and control water dating back to pre-European settlement days when Native Americans had erected simple dams for catching salmon.

Aquapedia background

Conjunctive Use

Conjunctive use is a catch-phrase for coordinated use of surface water and groundwater— literally going with the flow to maximize sufficient yield.

Aquapedia background

Colorado River 2007 Interim Guidelines And Drought Contingency Plans

In 2005, after six years of severe drought in the Colorado River Basin, federal officials and representatives of the seven basin states — California, Arizona, Nevada, New Mexico, Colorado, Utah and Wyoming — began building a framework to better respond to drought conditions and coordinate the operations of the basin’s two key reservoirs, Lake Powell and Lake Mead.

The resulting Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (Interim Guidelines) identified the conditions for shortage determinations and details of coordinated reservoir operations. The 2007 Interim Guidelines remain in effect through Dec. 31, 2025.

California Water Overview

Aerial view of the Sacramento-San Joaquin DeltaCalifornia will always be inextricably linked to its water resources. Water continues to shape the state’s development and no resource is as vital to California’s urban centers, farms, industry, recreation, scenic beauty and environmental preservation.

But California’s relationship to water is also one that continues to generate controversy.

Aquapedia background

Applied Water

Applied water refers to water delivered by an application to a user, either indoors or outdoors. Applied water use typically occurs in an agricultural or urban setting.

In agriculture, applied water is typically supplied through irrigation, which uses such devices as pipes and sprinklers. There are also different types of systems including gravity flow and pressurized systems.

With soil absorbing applied water and being porous (some water can move down below a plant’s root zone), it is necessary to apply more water than a crop might need.

Western Water Magazine

Overdrawn at the Bank: Managing California’s Groundwater
January/February 2014

This printed issue of Western Water looks at California groundwater and whether its sustainability can be assured by local, regional and state management. For more background information on groundwater please refer to the Founda­tion’s Layperson’s Guide to Groundwater.

Western Water Magazine

An Era of New Partnerships on the Colorado River
November/December 2013

This printed issue of Western Water examines how the various stakeholders have begun working together to meet the planning challenges for the Colorado River Basin, including agreements with Mexico, increased use of conservation and water marketing, and the goal of accomplishing binational environmental restoration and water-sharing programs.

Western Water Magazine

Adjusting to the New Reality: Climate Change in the West
July/August 2013

This printed issue of Western Water This issue of Western Water looks at climate change through the lens of some of the latest scientific research and responses from experts regarding mitigation and adaptation.

Western Water Magazine

Meeting the Co-equal Goals? The Bay Delta Conservation Plan
May/June 2013

This issue of Western Water looks at the BDCP and the Coalition to Support Delta Projects, issues that are aimed at improving the health and safety of the Delta while solidifying California’s long-term water supply reliability.

Western Water Magazine

Viewing Water with a Wide Angle Lens: A Roundtable Discussion
January/February 2013

This printed issue of Western Water features a roundtable discussion with Anthony Saracino, a water resources consultant; Martha Davis, executive manager of policy development with the Inland Empire Utilities Agency and senior policy advisor to the Delta Stewardship Council; Stuart Leavenworth, editorial page editor of The Sacramento Bee and Ellen Hanak, co-director of research and senior fellow at the Public Policy Institute of California.

Western Water Magazine

How Much Water Does the Delta Need?
July/August 2012

This printed issue of Western Water examines the issues associated with the State Water Board’s proposed revision of the water quality Bay-Delta Plan, most notably the question of whether additional flows are needed for the system, and how they might be provided.

Western Water Magazine

Levees and Flood Protection: A Shared Responsibility
May/June 2012

This printed issue of Western Water discusses several flood-related issues, including the proposed Central Valley Flood Protection Plan, the FEMA remapping process and the dispute between the state and the Corps regarding the levee vegetation policy.

Western Water Magazine

The Colorado River Drought: A Sobering Glimpse into the Future
November/December 2010

This printed issue of Western Water examines the Colorado River drought, and the ongoing institutional and operational changes underway to maintain the system and meet the future challenges in the Colorado River Basin.

Western Water Magazine

A ‘New Direction’ for Water Decisions? The California Water Plan
May/June 2010

This printed issue of Western Water examines the changed nature of the California Water Plan, some aspects of the 2009 update (including the recommendation for a water finance plan) and the reaction by certain stakeholders.

Western Water Magazine

Changing the Status Quo: The 2009 Water Package
January/February 2010

This printed issue of Western Water looks at some of the pieces of the 2009 water legislation, including the Delta Stewardship Council, the new requirements for groundwater monitoring and the proposed water bond.

Western Water Excerpt Gary PitzerRita Schmidt Sudman

Desalination: A Drought Proof Supply?
July/August 2009

It seems not a matter of if but when seawater desalination will fulfill the promise of providing parts of California with a reliable, drought-proof source of water. With a con­tinuing drought and uncertain water deliveries, the state is in the grip of a full-on water crisis, and there are many people who see desalination as a way to provide some relief to areas struggling to maintain an adequate water supply.

Western Water Magazine

Desalination: A Drought Proof Supply?
July/August 2009

This printed issue of Western Water examines desalination – an issue that is marked by great optimism and controversy – and the expected role it might play as an alternative water supply strategy.

Western Water Magazine

Dealing with the ‘D’ Word: The Response to Drought
November/December 2008

This printed copy of Western Water examines California’s drought – its impact on water users in the urban and agricultural sector and the steps being taken to prepare for another dry year should it arrive.

Western Water Magazine

A Drought-Proof Supply: The Promise of Recycled Water
July/August 2008

This printed copy of Western Water examines recycled water – its use, the ongoing issues and the prospects it holds for extending water supplies.

Western Water Magazine

Small Water Systems, Big Challenges
May/June 2008

This printed copy of Western Water examines the challenges facing small water systems, including drought preparedness, limited operating expenses and the hurdles of complying with costlier regulations. Much of the article is based on presentations at the November 2007 Small Systems Conference sponsored by the Water Education Foundation and the California Department of Water Resources.

Western Water Magazine

A Significant Challenge: Adapting Water Management to Climate Change
January/February 2008

This printed copy of Western Water examines climate change – what’s known about it, the remaining uncertainty and what steps water agencies are talking to prepare for its impact. Much of the information comes from the October 2007 California Climate Change and Water Adaptation Summit sponsored by the Water Education Foundation and DWR and the November 2007 California Water Policy Conference sponsored by Public Officials for Water and Environmental Reform.

Western Water Magazine

The Struggle to Secure Water in the Southwest
May/June 2007

This issue of Western Water asks whether a groundwater compact is needed to manage this shared resource today. In the water-stressed West, there will need to be a recognition of sharing water resources or a line will need to be drawn in the sand against future growth.

Western Water Excerpt Gary PitzerRita Schmidt Sudman

Smart Water Use: Stretching the Urban Supply
May/Jun 2005

Despite a winter during which much of California was drenched with plentiful rain and snow, there is no escaping the need for the continued wise use of water, no matter what the change of seasons brings.

Western Water Magazine

Smart Water Use: Stretching the Urban Supply
May/June 2005

This issue of Western Water examines the continuing practice of smart water use in the urban sector and its many facets, from improved consumer appliances to improved agency planning to the improvements in water recycling and desalination. Many in the water community say conserving water is not merely a response to drought conditions, but a permanent ethic in an era in which every drop of water is a valuable commodity not to be wasted.

Western Water Excerpt Sue McClurgRita Schmidt Sudman

Does California Need More Surface Water Storage?
Sept/Oct 2003

According to political debate and the popular press, the purpose of adding surface water storage reservoirs to California’s existing system is to provide water for urban growth and agricultural crops. But that viewpoint touches only the surface of a more complex policy and operations issue spelled out in the CALFED Record of Decision (ROD): the need to expand storage capacity to increase the existing system’s flexibility, improve water quality and provide water for fish, as well as meet the needs of a growing population.

Western Water Magazine

Does California Need More Surface Water Storage?
September/October 2003

This issue of Western Water explores the question of whether the state needs more surface storage, with a particular focus on the five proposed projects identified in the CALFED 2000 ROD and the politics and funding issues of these projects.

Western Water Excerpt Gary PitzerRita Schmidt Sudman

Tapping the World’s Largest Reservoir: Desalination
Jan/Feb 2003

“Water, water, everywhere, nor any drop to drink.” – Samuel Taylor Coleridge
For time immemorial, the seas of the Earth have been seen as an enticing but unreachable source of fresh water. Separating the salt from ocean water was always a cost prohibitive process, primarily reserved to wealthy Middle Eastern nations and small-scale operations such as ocean-bound vessels and small islands. Otherwise, through the evolution of modern civilization, man has depended upon lakes, rivers and groundwater – a supply that comprises less than 3 percent of the planet’s total water.

Western Water Magazine

Coping with the Threat of Terrorism
January/February 2002

The events of September 11 brought a new reality to the water world. Since California was the destination of the four hijacked planes, security was immediately tightened at dams, aqueducts and water treatment plants. This issue of Western Water examines the issue of water security and the preparedness of federal, state and local agencies to the threat of terrorism. In addition to physical security and bioterrorism, it focuses on the type of long-term security measures being implemented to ensure a safe water supply.

Western Water Excerpt Gary PitzerRita Schmidt Sudman

Drinking Water Challenges: A Roundtable Discussion
Jan/Feb 2001

Drinking water is the ultimate recycled resource. It is recycled over years, centuries and millenniums. The water we use today is the same supply with which civilization began. The water that once coursed down the Ganges River or splashed into Julius Caesar’s bathing pool may end up running from the tap in your home.

Western Water Excerpt Sue McClurgRita Schmidt Sudman

CALFED and the Delta Fix
January/February 1999

Balance between ecosystem restoration and water supply reliability is key to a Bay-Delta solution. Everyone agrees on this concept. But the demands of the competing interests can tilt the scales. So, too, can the member agencies’ conflicting missions. For more than three years, the joint state-federal CALFED Bay-Delta Program has been searching for equilibrium among the Delta’s complex problems and its contentious stakeholders. In December, it released its latest blueprint for resolving the Delta dilemma — the Revised Phase II Report.

Western Water Magazine

Cutting Colorado River Use: The California Plan
November/December 1998

This issue updates progress on crafting and implementing California’s 4.4 plan to reduce its use of Colorado River water by 800,000 acre-feet. The state has used as much as 5.2 million acre-feet of Colorado River water annually, but under pressure from Interior Secretary Bruce Babbitt and the other six states that share this resource, California’s Colorado River parties have been trying to close the gap between demand and supply.