WINNIPEG -- The Manitoba government has ordered an investigation into the susceptibility of Winnipeg's drinking water after a false E. coli result prompted a boil-water advisory last month for the capital's 700,000 residents.

City staff say they are confident the water system was not contaminated with bacteria, but the waste and water director says the province has ordered a further assessment.

"It's a vulnerability assessment," Diane Sacher told a city council committee Wednesday. "It's to look at whether our system is vulnerable to possible contamination."

That report is due at the end of April, she said. The city is also waiting on an independent audit of how water samples are taken and analyzed so as to be sure last month's results were due to a lab or sampling error.

A full report on what happened is expected in the next few weeks, Sacher said.

For two days in January, Winnipeggers had to boil their water after routine testing found coliform and E. coli at extremely low levels in six of 39 water samples. Businesses and residents were told that tap water was safe for bathing and laundry, but were advised to boil it for at least a minute before drinking it.

Subsequent tests all came back clean and there were no reports of anyone becoming ill from drinking or using tap water.

Officials suspected from the beginning that the initial test results were a false positive, but said they had no choice but to issue the citywide advisory.

The province has asked the city to look at whether it can better isolate neighbourhoods into zones to avoid future blanket advisories that could be unnecessary, Sacher said.

"We're looking into whether that is possible or not," she said. "That's an investigation that needs to happen."

The province has also amended the city's licence so water samples are no longer all collected on the same day, but rather spread over a week, she added. It has also requested the city come up with a better plan to notify potentially vulnerable people rather than relying on the media.

The city is looking at whether people can subscribe to an email notification service that would get advisories out more quickly, Sacher said.