The Department of Water and Power has recorded 34 'major blowouts' in Los Angeles' water system since Sept. 1 in which streets were flooded and pavement buckled. By contrast, the city had only 21 in September 2008, 17 in September 2007 and 13 in September 2006. City engineers are trying to determine what's causing the water main bursts, including pulling soil samples, sending pipe pieces to labs for testing and performing statistical analysis of each break. But some experts said a prime suspect should be the city's recent decision to ration water by allowing sprinklers to run only on Mondays and Thursdays. They say that if more water flows through the system on Mondays and Thursday when people are watering their lawns and then pressure suddenly drops on other days, it could put added stress on already aging pipes. 'You made a change in operations...and now you get an anomalous number of failures. To me that is an `ah hah' moment,' said Richard Little, director of the Keston Institute for Public Finance and Infrastructure Policy at the University of Southern California. Jean Pierre Bardet, chair of USC's engineering department who began informally consulting with DWP officials, concurred that water rationing should be thoroughly investigated, noting that the system's age makes it susceptible to problems. DWP officials said they are looking into the rationing, which began in June -- shortly before they noticed an uptick in major blowouts. There were 24 blowouts in July and 31 in August -- both increases from last year. 