Water Mains Under Stress

According to the report, on days when watering was allowed, water pressure in the pipes dropped. On days when watering wasn't allowed, pressure increased and "accelerated the metal fatigue failures of aged and corroded cast-iron pipes."

A blue-ribbon panel of scientists said that the high-volume water main breaks that bedeviled Los Angeles last summer and fall were caused in part by the city's restrictions on lawn watering, and their findings could force the city to remake its strict water conservation policy. The city last June limited the use of lawn sprinklers to Mondays and Thursdays, and those restrictions have proved highly successful. Officials said that in February, Los Angeles had its lowest recorded water use in 31 years.

But the water conservation policy was too much for the city's aging network of cast-iron pipes, causing fluctuations in water pressure that strained them to the bursting point, the panel's long-awaited report found. Its conclusions appear to put to rest other theories about the cause of the mystery, including increased seismic activity. According to the report, on days when watering was allowed, water pressure in the pipes dropped. On days when watering wasn't allowed, pressure increased and ''accelerated the metal fatigue failures of aged and corroded cast-iron pipes.''

The result was a series of major water main breaks that flooded streets and damaged property, starting weeks after the water restrictions took effect. From July through September 2009, the city recorded 101 major breaks, compared to 42 in 2008 and 49 in 2007, the report said.

The scientists suggested the city rework its conservation plan. One alternative would be to require homes with even-numbered addresses to conserve on even-numbered days and homes with odd-numbered addresses to conserve on odd-numbered days, the team said. That, they said, would help even up pressure.

Less than 72 hours later, another main burst in Valley Village, creating a sinkhole that swallowed half a firetruck that responded to the call. Firefighters crawled out the window to reach safety.

So far, the city has been hit with 108 legal claims regarding the Coldwater Canyon pipe breaks, 41 of them from homeowners, officials said Tuesday.

Of the latter number, 25 claims have been paid, two were denied, three have pending offers and 11 are awaiting more documents, said Assistant City Atty. Joseph Brajevich. The financial terms of those settlements were not immediately available.

The Times in September reported that some experts were speculating that water rationing had played a role in the water main breaks. But at the time, other experts were skeptical, questioning why water restrictions in L.A. would cause ruptures when other cities with similar rules, including Long Beach, were not experiencing the same problems.