- Colorado River: About 20% of Southern California's water comes from the Colorado River, which is brought to the region through the Colorado River Aqueduct.
- Northern Sierra: About 30% of Southern California's water comes from the Northern Sierra.
- Local supplies: The remaining 50% of Southern California's water comes from local supplies, including groundwater, recycled water, desalination, and the city of Los Angeles' eastern Sierra deliveries.
- Groundwater: Wells are dug into aquifers to access groundwater, which can then be pumped to the surface.
- Recycled water: Wastewater from homes and businesses is treated and recycled.
- Stormwater capture: Projects are being developed to capture stormwater and recharge groundwater.
- Climate change: Climate change and environmental enhancements are reducing the water supply.
- Drought: Low rainfall or light snowfall can lead to drought.