By 1:25 a.m., seven evacuees were at the school. Roughly an hour later, a Water Department official announced that water service had largely been restored.
The first sign of trouble came around 8 p.m. when neighbors began reporting seeing steam coming up through manholes - followed by gushing water.
Soon the streets were flooding. In some places, the water was knee-deep or higher with a south-flowing current.
Homeowners scrambled to seal basement windows with plastic. Firefighters used boats to rescue some stranded neighbors.
John DiGiulio, a spokesman for the Philadelphia Water Department, said crews had to shut down the 48-inch transmission main along 21st Street. It feeds water into smaller mains throughout South Philadelphia.
He said the action would affect a wide area, from Pine Street to the north all the way south to Oregon Avenue - and result in low pressure or a loss of water. But residents as far apart as 7th and Walnut streets and Packer Avenue in the stadium area reported their water had been shut off or was down to a trickle. Faucets at 13th and Walnut spat water that was cloudy and brown.
DiGiulio did not know how far to the east and west the shut-off would interfere with people's water supply. But he said water pressure was likely affected in homes many blocks away, including the Fairmount section to the north.
Neighbors reported that there had been construction in the area around 21st and Bainbridge. As for why the massive transmission main broke, DiGiulio said, "That is going to take some investigation. It's not our typical break season."
At 1:25 a.m. Monday, Dave Schrader, chief spokesman for the Red Cross' regional office, said a total of 38 people had had to leave their homes. He said seven were at the temporary center at the Stanton school, "getting food and water and coffee. Cots are also available if they choose to spend the night there."
By then, waters that had risen as high as three feet in streets around 21st and Bainbridge were down to a few inches at most.
DiGiulio said the painstaking process of completely shutting off the transmission main was completed at about 1:30 a.m. About an hour later, he announced that water was flowing again to the areas affected by the break.
"They might not have the best pressure," DiGiulio said, "but they should have water."
He said PGW crews had gone from house to house to make sure no water was getting into gas lines.
Starting Monday morning, DiGiulio said, Water Department inspectors would be in the neighborhood around the break site. He said residents who still don't have water should call 215-685-6300, the same number for reporting a water damage claim.
Schrader urged residents to throw out any food that had been soaked by flooding.
Contact Jennifer Lin at 215-854-5659, firstname.lastname@example.org, or follow on Twitter @j_linq. Inquirer staff writers Matt Katz and Jessica Parks contributed to this article.