Quenching Orange County’s Thirst: Where We Get Our Water

About 75% of the water used in Orange County is imported. Most years, about half of the imported water supply travels 444 miles down the California Aqueduct (part of the State Water Project) from the Sacramento Delta, and the other half flows 242 miles from Lake Havasu along the Colorado River Aqueduct.

This year, because of drought conditions in Northern California and surplus supplies on the Colorado, only about one-third of Orange County’s water is being provided by the State Water Project, with the Colorado River Aqueduct making up the difference. However, as the Central Arizona Project uses more and more Colorado River water in the future, Orange County will come to rely on the California Aqueduct for most of its imported water.

Most of Orange County’s local water comes from a huge groundwater basin which lies under the northern part of the county. The underwater reservoir is replenished by rainfall and natural runoff, supplemented by imported water. Cities in south Orange County, which have no groundwater reserves, rely almost entirely on imported water.

bout 75% of the water used in Orange County is imported. Most years, about half of the imported water supply travels 444 miles down the California Aqueduct (part of the State Water Project) from the Sacramento Delta, and the other half flows 242 miles from Lake Havasu along the Colorado River Aqueduct.

This year, because of drought conditions in Northern California and surplus supplies on the Colorado, only about one-third of Orange County’s water is being provided by the State Water Project, with the Colorado River Aqueduct making up the difference. However, as the Central Arizona Project uses more and more Colorado River water in the future, Orange County will come to rely on the California Aqueduct for most of its imported water.

Most of Orange County’s local water comes from a huge groundwater basin which lies under the northern part of the county. The underwater reservoir is replenished by rainfall and natural runoff, supplemented by imported water. Cities in south Orange County, which have no groundwater reserves, rely almost entirely on imported water.

COUNTY PROJECTED POPULATION/WATER DEMAND

Year Population Water Demand* Import 1990 2,306,700 657,000 63% 2000 2,676,900 753,000 66% 2010 2,831,100 838,500 68%

* Amounts in acre feet

Source: Municipal Water District of Orange County

HISTORIC PER CAPITA WATER CONSUMPTION IN ORANGE COUNTY

Municipal, Industrial Per Capita Water Use Estimated Consumption Rainfall Fiscal Year (acre feet) Population (GPCD) (inches) 1970-71 321,400 1,457,000 196 8.6 1971-72 361,200 1,531,000 210 4.9 1972-73 353,200 1,584,000 199 16.3 1973-74 371,600 1,646,000 201 11.5 1974-75 383,100 1,684,000 203 12.1 1975-76 415,600 1,729,000 214 7.2 1976-77 417,900 1,768,000 210 10.4 1977-78 389,100 1,815,000 191 28.5 1978-79 420,200 1,855,000 202 18.5 1979-80 452,800 1,921,000 210 21.2 1980-81 490,300 1,962,000 223 8.8 1981-82 462,500 2,002,000 206 13.1 1982-83 464,600 2,036,000 203 26.9 1983-84 461,300 2,066,000 199 9.0 1984-85 511,600 2,100,000 218 11.3 1985-86 *542,200 2,151,500 *225 15.4

GPCD--Gallons per capita per day

* Approximate

Source: Water Advisory Committee of Orange County; Municipal Water District of Orange County; Orange County Water District.

PRINCIPLE SOURCES OF LOCAL WATER AND ESTIMATED ANNUAL YIELD

Annual Source of Natural Supply Yield* Lower Santa River Basin -Runoff, local percolation 170,000 -Recharge 60,000 Total 230,00 Santiago Creek Runoff 7,500 San Juan Creek and ground water basin 10,500 La Habra Basin 6,000 -Ground water Santa Ana Mountains 1,000 -Ground water and runoff San Clemente 700 -Ground water TOTAL 255,700

Source of Natural Supply Location Lower Santa River Basin Located beneath northerly 40% of -Runoff, local percolation county, ground water basin is most -Recharge significant local water resource. Total Up to half of recharge is provided by imported water. Santiago Creek Runoff Surface runoff into Santiago Creek is stored in Irvine Lake. Most of the water is used for irrigation. (Annual flow 7,500 is long-term projection). San Juan Creek and Drains a 112,000-acre area in southern ground water basin county. Produces both potable and agricultural water. La Habra Basin Valley between Puente Hills and Coyote -Ground water Hills in northwestern county. Santa Ana Mountains -Ground water and runoff San Clemente -Ground water TOTAL

* In acre-feet (one acre-foot is 43,560 cubic feet, the quantity of water that would cover one acre to the depth of one foot. An average family of four uses about one acre-foot of water in a year)

Source: Water Advisory Committee of Orange County.