NEW ORLEANS (AP) — Officials say a boiler-room power failure at the plant supplying electricity to the city’s treatment plant is to blame for a temporary loss of water pressure.

The Sunday morning incident may have opened the way for water contamination. Officials are advising residents on the Mississippi River’s east bank to boil drinking water while samples from across the city are tested.

Most of New Orleans, including the French Quarter and Central Business District, is on the east bank.

Tap water was flowing again within an hour of the incident. The problem started about 9 a.m. Central time Sunday.

Engineers are investigating what caused the power failure.

It takes at least 24 hours to tell whether there are potentially dangerous bacteria in the water.