A boil water advisory in Saint John will remain in effect until at least Tuesday evening, say city officials.

The order was put in place on Saturday morning after one of the city's main water lines underneath Rothesay Avenue ruptured.

"The 24-inch cast iron water main, of 1873 vintage, was the pipe that had ruptured," said Kendall Mason, deputy commissioner of Saint John Water.

The age of the pipe was a major factor, he said.

Work crews replaced the broken section of pipe at about 4 a.m. on Monday, and started running water through the pipe at about 5 a.m., said Mason.

The boil water advisory can't be lifted until two consecutive water samples taken 24 hours apart come back clean, without any micro-organisms.

One sample has already been sent, said Mason.

Meanwhile, Rothesay Avenue remains closed between Russell and Reserve streets and at the intersection of Thorne Avenue, until crews can repair the broken asphalt where the rupture occurred.

Health risk low

About 35,000 people in the north end, uptown and south end are affected by the boil order.

Dr. Scott Giffin, the regional medical officer of health, says the main break raises the spectre of water-borne illnesses, such as salmonella and E. coli.

The organisms can cause diarrhea, cramps, nausea, headaches and other symptoms.

But the risk is low, he said.

"I know the question out there is, 'What would happen if I drank the water?' Chances are, nothing," Giffin said.

Residents in the affected areas, living west of Rothesay Avenue and Russell Street, are asked to bring their water to a rolling boil for at least a minute before drinking, brushing their teeth, making ice, juice, coffee, tea, or washing vegetables that won't be cooked.

Boiling kills bacteria and other organisms in the water.

It is safe to bathe with the water. It is also safe to wash dishes in the dishwasher, or by hand with hot, soapy water and then air dry.