The Philadelphia Water Department says the 30-inch main was 130 years old and burst around 12:45 a.m. Sunday near 6th and Bainbridge streets.
Viewer video captured the water rising several feet from the ground and gushing like a river.
"Basically rapids at the corner of 6th and Bainbridge," South Philadelphia resident Allitia DiBernardo said. "The water was coming out with such force it was like a whitewater gusher."
The massive crater at the heart of the break has become an attraction of sorts, some mesmerized by the sheer size of it.
"It looked like a miniature earthquake, and thank God no cars or nothing was there. Somebody could have gotten seriously hurt," said Julius Sumpter of West Philadelphia.
Firefighters had to go door-to-door telling people to shelter in place as water flooded basements.
Residents like DiBernardo and Charles Derr, like many around the impacted area, are now left to decide what stays and what will eventually end up on the curb.
"There was two feet in the basement," Derr said.
Sandy Ward, who's an interior designer and collector, believes she lost $1 million worth of art and furniture. The Action Cam was there when water knocked out her window and poured into her basement.
"It's my natural disaster. You know, this aging infrastructure in the City of Philadelphia, I'm not really surprised," Ward said.
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"It just seemed so scary, and the water was rising so fast," added resident Lara Rhame.
One neighbor says he saw a man fall into the hole in the ground. Luckily, he was able to claw his way back up.
Rob Czyzewicz, whose birthday was on Sunday, was left with his basement bedroom under three feet of water.
"I started hearing this gurgling sound coming from my bathroom and I went to see what it was; at first it was nothing, then five minutes later the water started exploding from the bathroom," Czyzewicz said.
While the flooding impacted several businesses for at least the day, some were spared the worst of the flooding, including the Mostly Books store on Bainbridge Street just feet from the main break
"Paper and water obviously don't mix, but it's a mess to clean because the paper falls apart and it's heavy," said business owner Sharon Bruce.
Utility crews spent the day working to assess the damage and connect with those impacted by the water damage.
Derr tried to see a positive in the disaster.
"I guess it's an opportunity to get rid of stuff," Derr said.
Officials with PWD said it's their goal to help homeowners clean and dry out their basements. Any property owner who needs assistance should call PWD's 24/7 customer service line at 215-685-6300.
At this time, no customers are believed to be without water. Road closures near the scene of the break should be expected until further notice.