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San Diego's upgraded Earl Thomas Reservoir—the world's largest, prestressed concrete reservoir—replaced a reinforced structure that had become unstable. Photo: City of San Diego Water Department

San Diego mayor Jerry Sanders and councilmember Jim Madaffer recently helped the San Diego Water Department dedicate the new Earl Thomas Reservoir at the Alvarado Water Treatment Plant. The reservoir is the largest, pre-stressed concrete drinking water reservoir in the world.

“The new reservoir is a wonderful and important addition to our city's water treatment system,” said Sanders. “This helps increase Water Department reliability, which is important to everyone in San Diego.”

The old, reinforced concrete drinking water reservoir was built in the 1950s and had the capacity to hold 35 million gallons. After 50 years of service, the reservoir became seismically unstable and required total replacement. In September 2002, the old reservoir was demolished and excavated to make room for the modern one and to help upgrade the plant. The new reservoir increases the Alvarado Water Treatment Plant's onsite drinking water storage capacity from 42 million to 77 million gallons.