As crews have fought the fast-spreading fires across the Los Angeles area, they have repeatedly been hampered by low water pressure and fire hydrants that have gone dry. These problems have exposed what experts say are vulnerabilities in city water supply systems not built for wildfires on this scale.

The water system that supplies neighborhoods simply doesn’t have the capacity to deliver such large volumes of water over several hours, said Martin Adams, former general manager of the Los Angeles Department of Water and Power.

“The system has never been designed to fight a wildfire that then envelops a community,” Adams said in an interview with The Times.

The limitations of local water systems complicated firefighting efforts in Pacific Palisades, where scores of fire hydrants were left with little or no water, and in Altadena and Pasadena, which are served by different utilities and where firefighters say they have grappled with low water pressure.

The local water supply system in the Palisades area is designed to flow with enough gallons a minute to fight a house fire or a blaze in apartments or commercial buildings, Adams said. “Then you have a massive fire over the whole community and you have 10 times as many fire units, all pulling water out of the system at once.”