Earlier this week a pipeline feeding into the Reading sewage treatment plant ruptured.
It's now estimated that as much as 75 million gallons of raw sewage poured into the Schuylkill River.
That's bad news for Pottstown and Philadelphia which get all or some of their drinking water from the river.
"We definitely want to protect the Schuylkill River as much as we can because the residents depend on it," Pottstown Borough Manager Jason Bobst said.
Pottstown is 15 miles downriver from Reading.
12,000 residents of the borough and surrounding communities get 100% of their drinking water from the river.
The water treatment plant was notified right away and they immediately boosted chlorine levels. Residents may notice a stronger chlorine taste for a while.
"We are going to continue with the higher chlorine levels for the next day or two," Bobst said.
Philadelphia gets 40% of its drinking water from the Schuylkill. It's treated at the Belmont and Queens Lane facilities.
The Water Department says it has increased monitoring of the water quality. So far, they say there's been no impact.
Reading recently got an emergency state grant to troubleshoot its treatment plant.
This is the second major spill in three years. In 2008, raw sewage flowed into the river for two and a half days.
The spill this week lasted 35 hours.
Philadelphia and Pottstown both say the water is now safe to drink.
The State Department of Environmental Protection is also monitoring the sewage.
They say, for now, there's no evidence of environmental damage.