More than 1 million Montreal residents can finally drink water from their taps -- the city's mayor says a boil-water advisory has been lifted.

Montreal Mayor Michael Applebaum held a press conference at 10:15 p.m. ET Thursday to tell residents that water sample tests conducted by the city came back clean.

“The water is of good quality, everyone can drink it,” Applebaum said, adding that if water looks slightly brown, resident should let the tap run a bit before pouring a glass.

The water crisis began Wednesday, when water flowing from the taps in the city began turning brown.

City officials said the problem derived from the Atwater water filtration plant, the country’s second-largest filtration plant, which is currently in its fourth year of extensive maintenance work.

For reasons still not clear, water levels in a reservoir dipped to an unusually low level on Tuesday during the renovation work. That stirred up sediment. Workers refilled the reservoir, but early Wednesday morning residents of St. Henri and Verdun complained about brown water from their taps.

Applebaum said city officials are carrying out an investigation to find out the cause of the problem at Atwater, which he said was not a result of a mechanical error.

“The objective here is to find out exactly what happened, how it happened and make sure it doesn’t happen again,” Applebaum said.

On Wednesday, the city issued a notice advising residents in those boroughs to bring their water to a rolling boil for 60 seconds before drinking or using the water for cooking, washing food or brushing teeth.

The advisory was expanded throughout the day as the full extent of the problem became known.

A number of residents said after seeing the brownish water coming from their taps, they decided to purchase bottled water instead.

“The water was quite cloudy … so I didn’t want to take a chance,” Kelly Albert, a resident of Verdun, told CTV Montreal.

Many residents rushed to stores, filling their shopping carts with cases of bottled water. At Wal-Mart, shoppers were out of luck as the giant retailer ran out.

At local schools, teachers were advised to close off drinking fountains.

The advisory also prompted some hospitals to shut off their water fountains. At the McGill University Health Centre, the cafeteria stopped using tap water while staff members handed out bottled water to patients.

Some local businesses also took precautionary measures. All Starbucks in the affected boroughs stopped selling coffee and tea. Only pre-bottled beverages and pastries were being sold.

With files from CTV Montreal and The Canadian Press