The affected area is bounded roughly by Rinaldi Avenue on the south, Balboa Boulevard on the east, De Soto Avenue on the west and the foothills and hills to the north, according to the DWP.
According to the agency, water crews were conducting repair work on Tuesday at a pump station that connects to a 10 million-gallon water tank that serves the area when a valve that controls the flow of water failed to open.
"As a result, the water flowing from the tank into the pipes serving the area was cut off," according to a DWP statement.
More than 9K LADWP customers remain without service amid water outage in Granada Hills, Porter Ranch
Crews immediately embarked on repair efforts, digging to reach the valve that is located about 20 feet underground. DWP officials originally said the repairs could take until Friday, but later said the project could "take through this weekend to be completed." The utility noted that the location of the broken valve also has two underground oil pipelines, a fiber optic line, gas line and large boulders that "have complicated repair efforts."
DWP officials said they were working on a possible temporary fix that would involve pumping water from a nearby Metropolitan Water District of Southern California facility into the DWP's 54-inch trunklink that feeds water to the affected area.
It was unclear when or if that temporary fix might be implemented.
Meanwhile, residents were left without reliable water service. The DWP issued a boil-water notice for the area on Wednesday, instructing residents to use only boiled tap water or bottled water for drinking and cooking. The notice affects DWP customers north of Rinaldi Street or the 118 Freeway, whichever is further north, and west of Balboa Boulevard.
Water outage in Porter Ranch, Granada Hills impacting thousands
The DWP established water-distribution sites providing drinking water to affected residents. The sites are at:
-- Holleigh Bernson Memorial Park, 20500 Sesnon Blvd., Northridge;
-- O'Melveny Park, 17300 Sesnon Blvd., Granada Hills; and
-- the intersection of Tampa Avenue and Sesnon Boulevard on the Northridge-Porter Ranch border.
Porter Ranch resident Wendy Moore was among the many who lined up at the Sesnon Boulevard distribution site on Thursday morning.
"I was told last night at 9:18 that they closed at 9," she told ABC7 on Thursday morning. "So -- and they opened at 7 -- and I'm number twenty-one. The line is -- I can't see the end of the line."
DWP officials said they were also installing portable showers, handwashing stations, mobile laundry units and portable toilets at all of the water-distribution sites. The water distribution sites are scheduled to be open daily from 7 a.m. to 9 p.m.
But on Thursday morning, Porter Ranch resident Kiran Walia was among those who expressed frustration that the Sesnon Boulevard distribution site did not open on time.
"It's already 7:08 and nobody's here, and they're saying 'Thank you for being patient,'" Walia said. "I mean, we all have to work, we have places to go, we have to tend to our kids. We have to live our normal life but this is hard to do."
By 7:30 a.m., the long line of cars was moving and water was being given out at the site.
Mayor Karen Bass also urged residents to take advantage of available cooling centers with restrooms during the outage. The centers are available at various Recreation and Parks facilities, with a list available at laparks.org/reccenter, and at public libraries, listed at lapl.org/branches.
"We recognize the loss of water to the area is a major inconvenience to our customers and we are doing everything we can to bring back the water to the area as quickly and safely as possible," DWP officials said in a statement Wednesday night. "We want our customers to know that our crews will work around the clock until repairs are made and we will continue to provide support and information throughout this incident."
The mayor's office noted that the Los Angeles Fire Department pre- deployed water tenders and engines in the affected neighborhoods, "with a focus on high-risk fire areas," and both LAFD and LAPD crews were "increasing proactive patrolling of the areas."
The water service outage occurred amid a growing heat wave that is expected to peak on Thursday, with many valley areas reaching triple-digits.
"While emergency repairs are underway, we are making drinking water, showers and other resources available for Angelenos who may have been impacted by the outage," Bass said in a statement. "Especially as we face rising temperatures, the LADWP and other City departments are mobilizing resources to ensure that Angelenos stay safe and hydrated."
Porter Ranch resident Jennifer Bronson also went to the distribution site at Tampa and Sesnon for water.
"There's nothing that I can do about it," she said of the service outage, adding that she would "just go ahead with anything I can do to conserve water and just get through this."
For the latest updates, visit www.ladwpnews.com.
City News Service contributed to this report.