In fact, California’s water systems leak less than those in some other parts of the country, particularly older Northeastern cities like Philadelphia and New York. But many of those have plentiful and cheap water. In drought states, the price of water has jumped, changing the calculations about the need to plug leaks.

That incentive makes a difference: As with most infrastructure issues, unless water is a problem — too much of it gushing across streets, too little of it in reservoirs — it goes largely unnoticed.

“We’re not spending enough on our infrastructure,” said Greg DiLoreto, a former president of the American Society of Civil Engineers and a retired chief executive of a water district in Oregon. Whatever money water utilities get, he said, “the first dollar will always go to safe drinking water” and not to pipes.

Los Angeles is paying close attention to its pipes, however. Its water agency targets lines with a history of leaking, and those in soil conditions that promote erosion. It also looks for pipes near critical facilities like hospitals, and in places with hilly terrain that could lead to violent flooding once the rogue water begins to flow. As the leak prevention program has been ramped up, the number of leaks in the system has dropped to 1,146 in the fiscal year 2013-14 from 2,031 in 2006-7.

“The key for us for replacement is to replace the right pipes,” said Marty Adams, who heads the water system for the Los Angeles Department of Water and Power.

Other California cities are finding that leak patrols pay off. Cloverdale, in northern Sonoma County, hired outside consultants to cut its losses. They tracked down a pipe with a crack that went all the way around it, gushing water. None came to the surface, where it would have been obvious; instead, it flowed into a nearby storm drain.