As a borderline arid region with an average of just 10 inches of rainfall annually, San Diego primarily relies on water imported from other regions to meet our freshwater needs. The water we use to brush our teeth, water our gardens, bathe our bodies, and keep us hydrated travels a long distance before it reaches us. Understanding where our water comes from is an important component of being a responsible water advocate.

Imported Water

Due to the region’s relatively dry climate, San Diego County imports over 80 percent of its water. More than half the water used in San Diego comes from a series of dams, canals, and pipes carrying water from the distant Colorado River. Despite its status as one of the the most endangered rivers in the United States, the Colorado supports the water needs of over 30 million people across California, Arizona, New Mexico, Nevada, Wyoming, and Colorado.

Another 30 percent of San Diego’s imported water comes from rivers fed by snowpack melting off the Sierra Nevada range – California’s mountainous backbone. This meltwater is diverted through the State Water Project – a vast system of aqueducts, canals, and dams – and pumped up and over the Tehachapi Mountains and distributed to urban areas across Southern California.

Local Water Sources

About 20 percent of San Diego County’s water supply comes from local sources, including capture of stormwater in and immediately around local reservoirs, small-scale and large-scale wastewater recycling, and ocean water desalination. Recent efforts to increase water conservation and improve water-use efficiency have helped to reduce the demand on water supplies. Water saved through conservation and more efficient use may either be stored and saved for later use, or kept in the natural environment for ecosystem protection and restoration.

Environmental Impacts of Water Supply

When humans move water out of the environment and into our water supply, there are inevitable environmental impacts. By diverting water from natural systems such as the Colorado River and rivers of northern California, river and stream flows are reduced, threatening endangered species populations and degrading essential habitat and ecosystems. The energy use associated with enormous water-moving projects is substantial, and produces greenhouse gases that contribute to climate change and changing precipitation patterns. Some water supply sources are more impactful than others. Desalination, for example, is associated with a host of environmental impacts from energy-intensivity to threats to marine life. Other forms of water supply may have fewer environmental impacts and provide benefits in addition to providing water. For example, wastewater recycling and stormwater capture are multi-benefit water supply sources that serve to reduce or prevent pollution while also providing locally-sourced freshwater.