Metropolitan Water District of Southern California

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Metropolitan Water District of Southern California
Water district overview
Formed 1928 (1928-MM)
Headquarters700 North Alameda Street, Los Angeles, California
Water district executive
  • Jeffrey Kightlinger, General Manager

The Metropolitan Water District of Southern California is a regional wholesaler and the largest supplier of treated water in the United States. The name is usually shortened to "Met," "Metropolitan," or "MWD." It is a cooperative, of fourteen cities, eleven municipal water districts and one county water authority, that provides water to 19 million people in a 5,200-square-mile (13,000 km2) service area. It was created by an act of the California Legislature in 1928, primarily to build and operate the Colorado River Aqueduct. MWD became the first (and largest) contractor to the State Water Project in 1960.

Metropolitan owns and operates an extensive range of capital facilities including the Colorado River Aqueduct which runs from an intake at Lake Havasu on the California-Arizona border, to an endpoint at Metropolitan’s Lake Mathews reservoir in Riverside County. It also imports water supplies from northern California via the 444-mile (715 km) California Aqueduct as a contractor to the State Water Project. Metropolitan operates sixteen hydroelectric facilities, nine reservoirs, 830 miles (1,340 km) of large-scale pipes, and five water treatment plants. Four of these treatment plants are among the ten largest plants in the US.

It serves parts of Los Angeles, Orange, San Diego, Riverside, San Bernardino and Ventura counties. The district covers the coastal and most heavily populated portions of Southern California; however large portions of San Diego, San Bernardino and Riverside counties are located outside of its service area.

The MWD headquarters is located at 700 North Alameda Street in downtown Los Angeles, adjacent to historic Union Station.


Drinking water pumping station near Parker Dam, 1972

The Metropolitan story dates back to the early 20th century, as Southern California cities were faced with a growing population and shrinking local groundwater supplies. The Metropolitan Water District of Southern California was established in 1928 under an act of the California Legislature to build and operate the 242-mile Colorado River Aqueduct (389 km) that would bring water to southern coastal areas. Southland residents voted for a major bond in the depths of the Great Depression to fund the construction effort through the desert to deliver essential water supplies and generate badly needed jobs.[citation needed]

The post-World War II boom and 1950s dry spells prompted a huge expansion of the Metropolitan service area as new cities began seeking additional reliable water supplies.[citation needed]

In 1960, Metropolitan, along with 30 other public agencies, signed a long-term contract that made possible the construction of the State Water Project, including reservoirs, pumping plants and the 444-mile California Aqueduct (715 km), which currently serves urban and agricultural agencies from the San Francisco Bay to Southern California. As the largest of the now 29 agencies, Metropolitan contracts with the state Department of Water Resources, which owns and operates the State Water Project, for slightly less than half of all supplies delivered to Metropolitan.[citation needed]

The MWD is governed by a board of 38 directors whose powers and functions are specified in the 1927 authorization act. This board was in charge of issuing bonds and financing their repayment by selling water to member agencies. In the early years, revenue from water sales was too low, so MWD also collected taxes that ranged from 0.25 to 0.50 percent of assessed value. Ninety percent of the cost of the aqueduct has been paid for by the taxpayers. In 1929 the district was set up with an area of 600 square miles (1,600 km2) and served a population of around 1,600,000 in 13 cities.[1]

During the aqueduct's first five years of service from 1941 to 1946 it delivered an average of about 27,000 acre feet (33,000,000 m3) of water, using less than 2% of its capacity. Only one pump at each lift, operating from one to six months out of the year, was needed to meet all the demands made on the system. At this time, due to availability of ground water, less than 10% of the Colorado River Aqueduct's capacity was used, only 178,000 acre feet (220,000,000 m3) of water. [2]

The San Diego County Water Authority joined MWD as its first wholesale member agency in 1946. SDCWA was formed in 1944 to facilitate joining MWD, received its first deliveries in 1947 and was buying half of MWD's water by 1949. The SDCWA annexation broke two traditions at MWD: Member agencies had previously been cities (SDCWA was a water wholesaler) in the south coast basin (SDCWA was south of the basin). The next "break" came in 1950, when Pomona MWD (now Three Valleys MWD) joined MWD. Since Pomona was a largely agricultural member agency at the time, MWD was no longer selling water only for "domestic use". [3] (The territory served by the Pomona district urbanized rapidly, with agriculture having disappeared almost entirely by 1970.)

In 1952, MWD began a 200 million dollar program to bring the Colorado River Aqueduct to its full capacity of 1,212,000 acre feet (1.495×109 m3) annually. The Colorado River Aqueduct added six pumps to the original three at each of its five pumping stations. CRA pumping expanded from about 16,500 acre feet (20,400,000 m3) of water in 1950 to about 1,029,000 acre feet (1.269×109 m3) by 1960. On August 9, 1962, the MWD set an all-time delivery record of 1,316,000,000 gallons of water in just a 24-hour period.[citation needed]

Met's additional supplies and easier rules of entry facilitated an expansion through annexation of large areas of low populations: The eight MWDs that joined from 1946 to 1955 added 200 percent to Met's service area but only 75 percent to Met's population served.[4] By 1965, Met had 13 cities and 13 municipal water districts as members. It covered more than 4,500 square miles (12,000 km2) in the counties of Los Angeles, Ventura, Orange, San Diego, Riverside, and San Bernardino—and served some 10,000,000 people.[citation needed]

As of 2008 Met has 14 cities and 12 municipal water districts (San Fernando joined in 1973; MWDOC and Coastal MWD merged in 2001) and provides water to nearly 10,000,000 people.[5]

Water sources[edit]

Colorado River Aqueduct

The State Water Project moves water from the Sacramento-San Joaquin River Delta, via the California Aqueduct to southern California. The water diverted from the Delta is provided via transfer at Lake Oroville on the Feather River. During the dry season Oroville Dam releases additional water into the Feather, which eventually flows into the Sacramento River and the Delta, allowing water diversion while maintaining a minimum freshwater outflow from the Delta to the Pacific. Once the California Aqueduct reaches southern California, it is split between the West Branch, storing water in Castaic Lake for delivery to the west side of the Los Angeles metropolitan area, and the East Branch, which delivers water to the Inland Empire and the south and east parts of the Los Angeles Basin.

The Colorado River Aqueduct begins at Lake Havasu, the reservoir of Parker Dam, and travels 242 miles (389 km) west to Lake Mathews. Water is first pumped 125 miles (201 km) uphill through a series of five pumping plants approaching Chiriaco Summit, then flows 117 miles (188 km) downhill towards Los Angeles.

Metropolitan contracts for about 2 MAF/Y (million acre feet per year) from the State Water Project (SWP) and 1.35 MAF/Y from the Colorado River Aqueduct (CRA), but actual delivery amounts depend on a conditions including hydrology, infrastructure and regulatory conditions . Between 1984 and 2004 the actual deliveries were 0.7 MAF/Y from the SWP and 1.2 MAF/Y from the CRA. The SWP allotment is rarely met, if at all, due to restrictions on the amount of water that can be pumped from the Delta. A minimum freshwater flow has to pass through the Delta in order to prevent salinity intrusion from San Francisco Bay, and the removal of freshwater from the Delta has also threatened multiple species, such as native chinook salmon.[6][7]

The Inland Feeder project[8] added a direct tunnel and pipeline connection from Silverwood Lake to Diamond Valley Lake and was completed in 2010.


The Metropolitan Water District of Southern California reservoirs store fresh water for use in Los Angeles, Orange, Ventura, Riverside, San Bernardino, and San Diego counties. These reservoirs were built specifically to preserve water during times of drought, and are in place for emergencies uses such as earthquake, floods or other events.

The MWD maintains three major water reservoirs. One is Lake Mathews located in southwest Riverside, California, with a capacity of 182,000 acre feet (224,000,000 m3) of water. Another is Lake Skinner located south of Hemet in Riverside County, its capacity is 44,000 acre feet (54,000,000 m3) of water. Diamond Valley Lake is their third and newest reservoir, with a capacity of 810,000 acre feet (1.00×109 m3) of water. This capacity is over twice as large as that of Castaic Lake, the next largest reservoir in Southern California maintained by the state Department of Water Resources.

The MWD partly funded the Brock Reservoir project with $28.6 million. In return for their contribution, California can each use 100,000 acre feet (120,000,000 m3) of water starting in 2016.

Purification and treatment[edit]

Interior of zeolite building at F. E. Weymouth plant

The Metropolitan Water District (MWD) operates five treatment plants:

  • Robert B. Diemer Treatment Plant[9] in Yorba Linda[10]
  • Joseph Jensen Treatment Plant[11] in Granada Hills, due to a multimillion-dollar expansion, it is believed to be the largest treatment plant west of the Mississippi River, delivering up to 750 million gallons per day.
  • Henry J. Mills Treatment Plant[12] in Riverside
  • Robert A. Skinner Treatment Plant[13] in Winchester, is now the second largest water treatment facility at MWD after its multimillion-dollar expansion, delivering up to 630 million gallons per day.
  • F. E. Weymouth Treatment Plant,[14] a 58,800-square-foot (5,460 m2) facility in La Verne

They collectively filter water for more than 19 million Southern Californians.[15] The MWD employs over 2,100 people to maintain and do research at these facilities,[citation needed] including scientists specializing in chemistry, microbiology, and limnology (the study of lakes and rivers).

Water purification proceeds through the following steps:[16]

  1. Screening with relativelly coarse sieves removes larger debris such as sticks and leaves.
  2. Primary disinfection with chlorine. Several of Metropolitan's treatment plants are now using ozone instead of chlorine as a primary disinfectant.
  3. Addition of flocculant chemicals such as ferric chloride and organic polymers to encourage smaller particles to clump together.
  4. Sedimentation to allow the clumps to settle out of the water.
  5. Filtration to remove remaining particles.
  6. Next, more chlorine is added to the water to disinfect and prevent any illness due to water-borne pathogens.
  7. Lastly, ammonia is added to the water to react with the chlorine to form chloramines. Chloramines are used to maintain a residual disinfectant throughout the water distribution system.
  8. After purification, sodium hydroxide is added to adjust the pH level to protect the pipes and plumbing fixtures, and fluoride is added to the water to help prevent dental caries in children.

Every year trained scientists and technicians perform more than 320,000 analytical tests on more than 50,000 samples.[citation needed] Metropolitan Water District has various EPA Environmental Protection Agency approved methods used to for the detection of bacteria, viruses, protozoan parasites, chemical contaminants and toxins.


MWD list of member agencies:

See also[edit]


  1. ^ The Great Aqueduct: The Story of the Planning and Building of the Colorado River Aqueduct (PDF). The Metropolitan Water District Of Southern California. 1941. Retrieved 21 September 2016.
  2. ^ Erwin Cooper, Aqueduct Empire: A Guide to Water in California, Its Turbulent History and Its Management Today, The Arthur H. Clark Company, Glendale, California 1968. pp 87-89
  3. ^ David Zetland (2008), Conflict and Cooperation within an Organization: A Case Study of the Metropolitan Water District of Southern California. PhD Dissertation, UC Davis. pp. 13, 28-32.
  4. ^ David Zetland (2008), Conflict and Cooperation within an Organization: A Case Study of the Metropolitan Water District of Southern California. PhD Dissertation, UC Davis. p. 32.
  5. ^ Metropolitan Water District of Southern California
  6. ^ David Zetland (2008), Conflict and Cooperation within an Organization: A Case Study of the Metropolitan Water District of Southern California. PhD Dissertation, UC Davis. pp. 37-38.
  7. ^
  8. ^ Inland Feeder link at MWD
  9. ^
  10. ^
  11. ^
  12. ^
  13. ^ "Archived copy". Archived from the original on 2006-12-11. Retrieved 2007-02-16.CS1 maint: Archived copy as title (link)
  14. ^
  15. ^
  16. ^ The Story of Your Water

External links[edit]