“To the people of Pittsburgh, we’re sorry that this happened.” Pittsburgh Mayor Bill Peduto said. “We had to be cautious, we had to take precautionary measures. At no time was your water ever in danger.”Schools also re-opened Thursday after the water safety concerns led to multiple school closures and water use restrictions throughout the city.

PWSA officials told Fox News the advisory to flush and boil tap water affected 100,000 residents.

Schools under the advisory took measures to cover up water fountains and provide hand sanitizer to students who did not want to use the water to wash their hands, Pittsburgh Public Schools said in a statement.

Peduto noted that the PWSA has been neglected over the past decade.

“This authority has never been given the proper resources to be able to succeed” Peduto said.

He mentioned his intention to work on the city’s infrastructure.

“You can’t go back and then rebuild a system that will be safe under this existing structure,” Peduto said.

Pennsylvania’s Department of Environmental Protection raised concerns about the city’s water filtration after tests showed low chlorine levels, which presented a potential for contamination. City officials reminded the public the water restrictions were issued out of an abundance of caution. Testing showed no threat to public health.

Robert Weimar, PWSA’s interim director of engineering, specified the violation was found in the second filtration treatment process. He added that PWSA has tested the water for Giardia–a main water contaminant–and they have not found signs of the parasite.

More than a dozen water distribution sites were placed throughout the city during the advisory period.