One hundred years after its opening, the Los Angeles Aqueduct continues to cast a long shadow over the rough and tumble of California water policy. The arrival of water from the Owens Valley made the modern city possible. But it also reshaped Los Angeles to suit its capabilities and changed water politics forever.

The aqueduct was not designed to bring water to Los Angeles but rather to the arid wasteland of the San Fernando Valley, which then lay outside the city limits. This would vastly enrich the lands owned by a small band of prominent industrialists who were promoting the aqueduct. To prevent this group from profiting from the public project, President Theodore Roosevelt prohibited Los Angeles from selling any of the Owens Valley water outside the city limits. Los Angeles promptly resolved that difficulty by annexing the San Fernando Valley, thereby cementing an often fractious relationship between the two communities.

Exclusive access to the aqueduct has given Los Angeles a much purer and less costly water supply than its neighbors, who must rely on supplies drawn from saltier sources that require much more expensive treatment. Through the creation of the Metropolitan Water District, Los Angeles today has access to much more water than it needs. But its continued reliance on the superior supplies from the Owens Valley means that the water Los Angeles hasn't used from the water district has been available to support the development of Orange County and San Diego....