Mississippi health officials told residents in the state’s capital to boil their tap water Thursday after traces of E. coli bacteria were found in the city’s supply — a result the manager of Jackson’s long-troubled water system disputed while calling it a devastating setback for rebuilding public trust.

The boil water notice, which officials also imposed in the Jackson suburb of Flowood, was issued just days before the expected arrival of a blast of cold weather that could further disrupt the local water infrastructure. The bacteria’s presence indicates that the water may be contaminated with human or animal waste, the state health department said.

Residents of the two Mississippi cities were advised to boil their water for one minute before using it. The precaution will last at least two full days as officials collect new samples for testing.