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Facts About California's Water

Water Supply

  • An acre-foot of water is equivalent to 325,851 gallons, or enough water to supply two typical families for a year.
  • It takes 3.3 acre-feet of water to grow enough food for an average family for a year.
  • Outdoor irrigation consumes about three quarters of the water provided to property owners in our service area.
  • California will be chronically short of water unless steps are taken now to improve our water supply system.
  • A water storage project typically takes 10 to 20 years to design and build.
  • Precipitation varies widely from year to year. In average years, close to 200 million acre-feet (MAF) of water falls in the form of rain or snow in California.
  • Over half of that water soaks into the ground, evaporates or is used by native vegetation. That leaves somewhere around 82 million acre-feet of usable surface water in average years. Of that water:48% goes to environmental uses such as instream flows, wild and scenic river flows, required Delta outflow and managed wetlands.41% is used by agriculture9% is used by cities and industry.
  • About 75% of California’s available water occurs north of Sacramento, while about 80% of the demand occurs in the southern two-thirds of the state.
  • Most of the rain and snowfall occurs between October and April, while demand is highest during the hot and dry summer months.
  • Groundwater provides about 40% of the state’s water supply. In dry years, that percentage can go as high as 60%.
  • California is prone to both droughts and floods. The most recent prolonged dry spell was a five-year drought from 2011 to 2016.  The previous prolonged dry spell was a six-year drought from 1987 to 1992. The most severe drought on record occurred in two consecutive years, 1976 and 1977, in which California received very little precipitation and surface water reservoirs were extremely low.

Water Delivery

  • California's communities, farms, businesses, and environment rely on water from a variety of sources. Surface water projects, which capture and deliver rain and snow runoff, provide a major portion of the state's total water supply. The projects include more than 1,000 federal, state and local reservoirs and conveyance systems.
  • Two of the most important projects are the federal Central Valley Project (CVP) and the State Water Project (SWP). The CVP and SWP bring water from Northern California through the Sacramento-San Joaquin River Delta for delivery to users in the San Joaquin Valley, parts of the San Francisco Bay Area and Southern California.
  • Key water projects and the amount of water they deliver:Central Valley Project (federal) -- 7 MAFState Water Project (state) -- 2.3 MAFAll-American Canal (local) -- 3 MAFColorado River Aqueduct (local) -- 1.2 MAFLos Angeles Aqueduct (local) -- 200,000 AFMokelumne Aqueduct (local) -- 364,000 AFSan Francisco Hetch Hetchy Project (local) -- 330,000 AF

The Role of Local Water Agencies

  • Local water agencies perform a number of functions to deliver water to California’s cities, farms and businesses.
  • Many agencies purchase water from the major state and federal water projects. They then treat the water as needed, and deliver it to their customers.
  • Some agencies operate their own local water supply systems, including reservoirs and canals that store and move water as needed.
  • Some agencies rely on groundwater exclusively, and operate local wells and distribution systems.
  • In recent decades, local agencies have developed more diversified sources of water supplies. Many agencies use a combination of imported surface water and local groundwater. They also produce or purchase recycled water for use in irrigating golf courses and other landscaping.
  • Many coastal agencies are pursuing ocean desalination projects to further diversify their water supplies or for use on brackish groundwater.
  • Some agencies have worked out water transfer agreements in which they purchase water from other agencies.
  • Urban and agricultural agencies have invested billions of dollars in water conservation and water use efficiency programs that reduce demand for water. Today, urban Southern California is using less water than it did a few decades ago, even though its population has grown tremendously.
  • Water agencies throughout the state are moving toward integrated regional water management planning, which generally includes a mix of programs such as water recycling, water use efficiency, groundwater management and conjunctive use, water transfers, flood protection and watershed management.
  • In addition to providing water supplies, many local water agencies have responsibility for providing local flood control and flood protection. Some are responsible for managing and replenishing groundwater basins, while others also treat wastewater.