Hundreds of thousands of people in Winnipeg, Manitoba have been advised to boil tapwater before they drink or cook with it after routine city testing indicated the presence of the sometimes deadly E. coli bacteria. Additional tests by the city conducted on Wednesday found no bacteria, but the warning remains in effect.

City officials said Wednesday afternoon that they are waiting for the results of a second round of tests, expected to arrive Thursday, before they lift the advisory. Until then, the advisory remains in effect for 700,000 people in the Canadian city.

The announcement of the advisory Tuesday night was the first time in recent history that Winnipeg has seen official warnings against drinking tap water. It isn’t clear what caused the initial positive test for E. coli or how the bacteria, which are often found in human or animal feces, might have entered the water supply. Cases of E. coli contamination in other cities sometimes stem from failures at sewage treatment plants.

The advisory sent residents of the city rushing to stores to buy bottled water Wednesday.

“It’s very important we do our part to communicate to friends and family that this is a precautionary boil-water advisory and there have been no injuries,” Winnipeg Mayor Brian Bowman told reporters, praising media outlets for spreading the word.

“I was having some coffee and some tea this morning, and I boiled it,” the mayor added, stressing that he boiled it “for over a minute,” following the advisory’s guidelines.

The water advisory forced Winnipeggers to change their routines on Wednesday.

Crystal Snow, a shift supervisor at Earls, a local restaurant and bar that serves burgers and sushi, said she arrived at work Wednesday morning and directed staff to comply with the boil-water advisory. “Our menu hasn’t changed. We’re just trying to take every precaution to make sure that every part of the advisory is being observed,” Snow said.

Coffee and ice, however, are off the bill of fare. Boiling water in large quantities is difficult and potentially ineffective, Snow explained, so she’s been sending out runners to buy jugs of bottled water.

Instead of fountain soda drinks, which are connected to the public water supply, the restaurant offers cans of fizzy drinks, Snow said. And when a customer orders a glass of water, the staff brings out the bottled water to demonstrate that it is adhering to safety standards. The jugs are an unexpected expense, Snow explained, but “it’s either that or not operate.”