Why It's Not Just the Drought

Where Does LA's
Water Come From?

If someone asked you where you get your water, would you know how it got to your faucet or sprinkler? Water travels a long distance before arriving to individual users.

Understanding the sources and the routes it takes to reach your home is key to understanding the state of water in Los Angeles.

A 2013 report by the USC Center for Sustainable Cities found that in the city of Los Angeles, water comes from three main sources: the Owens River, Northern California and the Colorado River, and groundwater.

Owens River

The Owens River, Mono Lake Basin, and reservoirs in the Sierra Nevada Mountains provide 430 million gallons of water to the city of Los Angeles daily via the Los Angeles Aqueduct. This represents only about one-third of Los Angeles' water supply.

Northern California
and the Colorado River

Accounting for one-third of California’s total water supply, the Sierras are the state's largest source of water. When rain falls in the winter at higher elevations, it becomes snow. When that snow melts in the springtime, the melted water becomes runoff and flows into aqueducts and groundwater.

The Colorado River Aqueduct can deliver 1 billion gallons of water per day to cities in Southern California. In order to conserve the Sierras snowpack, more water is being imported from the Colorado River. About half of Los Angeles' water flows from the Colorado River via the Colorado River Aqueduct.


Groundwater, the water that collects on the ground either from rainwater or waste, accounts for 30% of California’s water supply. The use of groundwater is dependent on location: some areas have easy access to groundwater, while others rely on surface or imported water.

In the city of Los Angeles, groundwater represents close to one-tenth of the water supply. Seventy-percent of the city's water supply once flowed through the Los Angeles Aqueduct. Now, over 50% flows through the Colorado River Aqueduct, which can deliver 1 billion gallons of water per day to Southern California.

Of California's water, just 10% goes toward residential use, while half goes to the environment (e.g. rivers and lakes). The remaining 40% goes to agriculture.

Why Are We
Running Out?

Climate, for one, is a major culprit. With California experiencing warmer fall and winter temperatures and less rain, snowpack levels are 5% less than what is considered normal. However, when rain does occur, with no significant way to collect that water and reuse it, about 80% of rainfall gets dumped into the ocean.

This represents a significant issue regarding infrastructure. At one time, the Los Angeles River used to be a main source of the city’s water; however, in 1940 the city was concerned about flooding and needed a way to properly drain excess water. The river was restructured as a drainage system; water that was once useable began to be diverted into the ocean and the city lost a source of its drinking water.

“Water has always flowed into the ocean, but what we’re realizing now is that we need to capture it” says Kelly Sanders, Assistant Professor at the USC Viterbi Sonny Astani Department of Civil and Environmental Engineering.

Another reason that our sources are running low is due to water leaks and evaporation in the water transport system. When water moves from the Colorado River or the Sierras, through an aqueduct to Southern California, water can leak out of the aqueduct into the ground or is simply evaporated. A significant amount of water can be lost in the water delivery systems. In late 2015, the city of Los Angeles implemented “Shade Balls” to its reservoirs to assist in controlling water quality as well as save 300 million gallons of water per year from evaporation.

A large residential population has also stressed the water supply.

“More people means that there are more demands, at the same time that factors such as drought and higher temperatures have resulted in less supply” says Sanders.

Droughts are cyclical. Southern California last experienced one in 1985 that lasted for six years, while others in the distant past have lasted much longer. Sanders says “the current drought situation us one of the driest and hottest season, it could end soon or it could last a long time.”

Therefore, cities, states, and citizens should not look to a short‐term solution, but should think long-term conservation. Understanding where our water comes from and where it is going is an important step in understanding how to survive drought years.

What Can We Do About It?

Some promising solutions are being developed by the faculty at the USC Viterbi School of Engineering

Click on each professor's photo to learn more.