06/06/2013 01:49 EDT | Updated 08/06/2013 05:12 EDT

Boil-water advisory caused by series of unfortunate events, mayor says

Montreal mayor Michael Applebaum said today that last month’s boil-water advisory was nothing more than an “unpredictable and simultaneous chain of unfortunate events” at the Atwater treatment facility.

"I would like to note that the investigation ruled out professional error," Applebaum said at a news conference called to explain what, exactly, went wrong.

The city issued a boil-water advisory to 1.3 million Montrealers which lasted 36 hours, until tests showed the tap water was safe to consume.

He said workers involved in renovations at the aging Atwater water treatment plant were draining a reservoir when they removed a membrane, which caused the water to drain too quickly. Then, a supposed fail-safe pump that’s meant to kick in when the water gets low, failed.

It’s the first time in 100 years that an event of this magnitude happened at the Atwater facility, the mayor said.

The challenge: reaching residents without landlines

While the city's investigation ruled out human error, officials said staff will get more training and improvements will be made to the city's emergency mass-communication system.

Many residents complained that they learned about the boil-water advisory from the media and by word-of-mouth, in some cases several hours after the boil-water advisory had been issued.

Residents with a landline did get an automated call from the city. However, officials admit they need to find a reliable way to reach those who only have mobile phones.

"We talk about radio, we talk about television, we talk about also social media," said Applebaum. "What we want to do is build stronger partnerships, so that we could get out the message even quicker."