About 100,000 Pennsylvania American Water Company customers southwest of Pittsburgh are being asked not to drink or cook any water straight from the tap for the next 48 hours.
Penn American shared the news on its website around 5 p.m. Monday.
The water is safe for bathing and washing clothes, according to the post.
Affected communities in Allegheny County include Bethel Park, Clairton, Dravosburg, Elizabeth Township, Elizabeth Borough, Glassport, Jefferson, Jefferson Hills Borough, Liberty, Lincoln, North Fayette, South Fayette, South Park, Upper Saint Clair and West Elizabeth, as well as 41 others in Washington County.
Boiling kills bacteria and other organisms in the water, officials said.
Penn American reported that water samples taken earlier in the day from portions of its Allegheny and Washington county service areas showed cloudiness levels above the regulatory standard, which carries an increased risk for disease-causing organisms.
"We anticipate resolving the problem by this (Monday) evening," wrote Walters.
"Pennsylvania American Water is collecting and analyzing additional water quality samples, including bacteria samples.
We will inform you when tests show no bacteria and you no longer need to boil your water."
Another 100,000 PWSA customers in the East End faced one after disinfection and chlorine testing in January near the Highland Park filtration plant tested abnormally.