What is the primary source of water supply in California?

The primary source of water supply in California is surface water from rivers and reservoirs. This is particularly significant due to the state's geography and climate, as California has an extensive network of rivers and an intricate system of reservoirs designed to capture and store runoff from rainfall and snowmelt in the Sierra Nevada mountains.

Surface water provides a large share of the state's supply for agricultural, municipal, and industrial uses. Major rivers, such as the Sacramento and San Joaquin, play a critical role in this supply system, especially during the wet season when runoff peaks. The infrastructure for managing surface water, which includes dams, canals, and aqueducts, has been developed over many decades to ensure availability and distribution across various regions of California.

While groundwater, desalination, and rainwater harvesting are important sources of water supply, especially during times of drought or in specific regions, they do not serve as the primary source when considering the overall water supply in California. Groundwater, for example, is a vital backup and is heavily relied on, particularly during dry years. However, surface water remains the predominant source for the majority of California's water needs.