TORONTO -- As the May long weekend approached 20 years ago, an invisible killer began stalking the unsuspecting town of Walkerton, Ont., preparing to unleash an epidemic that would damage or destroy many lives.

Dangerous bacteria had found their way into a vulnerable well, flowing into a municipal water system dangerously low on chlorine and on to the taps from which the community of 5,000 drank. People began writhing in agony. The town's lone hospital was quickly overrun. Public health authorities frantically searched for a cause.

By the time E. coli O157:H7 bacteria in drinking water had been identified as the culprit, seven people had died and about 2,300 others had fallen ill.

An event was scheduled for last week to mark the 20th anniversary of that tragic weekend, but it was cancelled due to COVID-19.

"It's unfortunate," says Phil Englishman, a resident who attributes a stroke to E. coli poisoning. "It would have been a celebration of the town: We survived this thing, just like we're surviving this COVID-19 pandemic. In spite of the water, people in the town have pulled together."

As COVID has done now, the drinking water contamination back then forced the closure of town schools and restaurants. There was a run on bottled water. The acrid smell of bleach for washing hands and disinfection permeated the air. Amid fear, shock, deep sorrow and anger, pointed questions rose about what had gone wrong.

Finding the answers fell to Dennis O'Connor, then a justice of the Ontario Court of Appeal. He would lead a far-reaching public inquiry into the tragedy that he promised would leave no stone unturned.

"He started to restore the faith that we had that there was a path forward," said Bruce Davidson, a resident who would embark on a career of environmental activism. "He was the first person in authority that we actually believed and felt wasn't misleading us for their own purposes."

O'Connor's inquiry team spent more than a year ferreting out both the specific and systemic failures that had led to the first E. coli outbreak in a treated municipal water system. Among them were poorly trained water-system operators with no inkling that deep-well water could become contaminated and who played hard and fast with the rules.

Nor was anyone locally watching the well-regarded brothers who ran the water system. Neither were the poorly resourced government inspectors, who failed to take decisive action to deal with the repeated infractions they did find. Few anywhere, it seemed, had any real awareness of the threat farm runoff posed to the drinking water.

"We really didn't give any of that thought to the water," says Davidson. "We had in our minds cleaved it off and said, 'Death and serious injuries from water are exclusively reserved for impoverished countries, not for Canada. We have too much water and we're too smart for that'."

The inquiry would ultimately come up with scores of recommendations. Unlike with many such endeavours, all would eventually be implemented, something O'Connor allows is "enormously satisfying."

The political crisis sparked by the E. coli nightmare and ensuing inquiry would prompt sweeping and standard-setting legislative reforms: Laws replaced guidelines covering the protection of water sources, treatment standards, operator training and certification, testing procedures, laboratory accreditation and incident reporting.

The brothers who had run the system -- Stan and Frank Koebel -- were criminally convicted for falsifying well log entries.

Today, the tragedy is far from top of mind for most in the midwestern Ontario community. The post-crisis Walkerton Clean Water Centre on the edge of town, a top class training and resource facility, is a point of pride, a visible sign of how far the town has progressed on its "journey from infamy to excellence," as Davidson puts it.

But there is concern, too, that some of the lessons Walkerton taught the country are slowly being forgotten. For one thing, many municipal water systems in numerous communities aren't covered by mandatory water-source protection plans.

"I've been alarmed about all these many, many towns, villages and hamlets all over the province who don't have central treated drinking water systems but are just as vulnerable as Walkerton was, or more vulnerable," says Theresa McClenaghan, who heads the Canadian Environmental Law Association. "There are zero barriers for them. Most people don't know about that."

In addition, roughly 1.6 million people in the province rely on non-municipal drinking water sources that have few legislated protections.

"What I'm seeing is creeping governmental complacency about drinking water safety," said McClenaghan's colleague, Rick Lindgren.

For now, at least, the people in Walkerton prefer to dwell on the positives that flowed from the disaster. The community, residents say, has become more tightly knit, more aware, more connected with the rest of the world.

O'Connor agrees the town has much to be congratulated about two decades after those frantic dark days. But, he notes, not everyone might be in the mood for celebration.

"We shouldn't forget the sad part of it, too. That's not gone away completely," O'Connor says. "There still are families that are living with the tragedy. People still live with the consequences."

This report by The Canadian Press was first published on May 15, 2020