Because San Diego does not have enough water locally to serve its population, most water is imported. This means that San Diego must purchase the water. San Diego purchases its imported water from the San Diego County Water Authority, which in turn purchases the water from the Metropolitan Water District of Southern California.
- The Metropolitan Water District of Southern California (MWD) was formed in 1928 to import water from the Colorado River, initially, to cities in Los Angeles and Orange counties. As a result, it built and operates the Colorado River Aqueduct. Today, MWD gets its water from both the Colorado River and the State Water Project, and has 26 member agencies serving more than 18 million people.
- The San Diego County Water Authority (CWA) was created in 1944 and became a member agency of the Metropolitan Water District of Southern California (MWD). In 1947, CWA completed a pipeline connecting San Diego County with MWD's water supply. CWA has since completed more pipelines to better connect the County to its water supplier. CWA now has 24 member agencies in San Diego County, including the City of San Diego.
Bringing water to the people of San Diego is an expensive process. Some of the major costs of water include energy to pump the imported water from its sources, and constant infrastructure maintenance and improvements. In addition, the cost of water as a commodity continues to rise. The City must also treat drinking water to meet state and federal regulations for safety and quality.