San Diego, a mere quarter century ago, imported 95% of its water. Now, it brings in 57% ,and that number is expected to fall to 18% in the next two decades. MarketWatch staffer Jim Carlton takes a look at the how the city has changed it's ways to become a model for water use.

Following a severe drought in 1991, the city decided that never again would it be so vulnerable. In order to become better equipped, San Diego invested $2 billion to help the city wean itself off imported water.

One technique that San Diego and other cities used it to patch leaks to augment water supplies:

Their techniques include installing corrosion-resistant valves on water lines and deploying teams of inspectors to detect leaks. As much as a trillion gallons of water is wasted annually to household leaks in the U.S. alone, or enough to supply more than 11 million homes, according to the Environmental Protection Agency.

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