About 75% of the water used in Orange County is imported. Most of that water is stored in huge reservoirs outside the county, such as Lake Mathews in Riverside County at the terminus of the Colorado River Aqueduct (182,000 acre-feet) and Lake Perris, also in Riverside County, at the terminus of the California Aqueduct (128,000 acre-feet). Following is a list of Orange County reservoirs storing potable water, of which only Irvine Lake (also known as Santiago Reservoir) provides significant long-term storage.
Name: Irvine Lake** Location: North Irvine *Capacity: 25,000 Ownership: Irvine Ranch Water District, Serrano Irrigation District
Name: Upper Oso Reservoir** Location: Mission Viejo *Capacity: 3,800 Ownership: Santa Margarita Water District
Name: San Joaquin Reservoir Location: Newport Beach *Capacity: 3,051 Ownership: Irvine Ranch Water District, Mesa Consolidated Water District, South Coast County Water District, Huntington Beach, Newport Beach, Laguna Beach County Water District, Metropolitan Water District
Name: Walnut Canyon Reservoir** Location: Anaheim Hills *Capacity: 2,800 Ownership: Anaheim Name: El Toro Location: Mission Viejo *Capacity: 730 Ownership: El Toro Water District, Municipal Water District of Orange County Name: Big Canyon Location: Newport Beach *Capacity: 600 Ownership: Newport Beach Name: Portola Reservoir Location: Mission Viejo *Capacity: 580 Ownership: Santa Margarita Water District Name: Orange Reservoir Location: Brea *Capacity: 212 Ownership: La Habra, Brea, Fullerton Name: Palisades Reservoir Location: Dana Point *Capacity: 148 Ownership: Tri-Cities Municipal Water District Name: Olive Hills Location: Anaheim *Capacity: 184 Ownership: Anaheim * In Acre feet; an acre foot equal 43,560 cubic feet.