It happened just before 3:00 p.m. in the 2000 block of West Boston Street.
PGW said a total of 52 people were evacuated by the Philadelphia Fire Department, including 40 adults and 12 children, after a private contractor accidently struck the four-inch main.
The evacuations were a precaution, PGW said, noting that the leak was not inside a home.
About an hour later, 32 people were allowed home, but the remaining 20 were still evacuated.
PGW said it remains on scene working to seal the leak.