BURTCHVILLE TOWNSHIP, Mich. (AP) — Authorities posted a boil-water advisory Saturday for more than 900,000 people in southeastern Michigan but then eased it hours later to 13 communities.

The Great Lakes Water Authority reported a break on a critical pipe in St. Clair County, which carries treated water from Lake Huron and is the largest in the system.

“A loss of pressure can lead to bacterial contamination in the water system. … Boiling water before using it will kill bacteria and other organisms that may be in the water,” the agency, known as GLWA, said.

GLWA initially said roughly two dozen cities and townships were affected by the boil recommendation. But it reduced the number when it learned that water pressure didn’t fall below a certain threshold in some areas, including Pontiac, Rochester Hills, Sterling Heights and Troy.

Flint said it switched to a different water source.