Walkerton is a relatively small community. At the time of the event Stan Koebel was manager and Frank Koebel was water foreman. Neither had any formal training in his position, retaining their jobs through three decades of on-the-job experience. The water supply became contaminated with the highly dangerous O157:H7 strain of E. coli bacteria, from farm runoff into an adjacent well that had been known for years to be vulnerable to contamination.
Starting 11 May 2000, many residents of the community of about 5,000 people began to simultaneously experience bloody diarrhea, gastrointestinal infections and other symptoms of E. coli infection. For days the Walkerton Public Utilities Commission insisted the water supply was "OK" despite being in possession of laboratory tests that had found evidence of contamination. On 21 May, an escalation in the number of patients with similar symptoms finally spurred the region's Medical Officer of Health, Murray McQuigge, to issue a boil water advisory, warning residents not to drink the tapwater.
Seven people died directly from drinking the E. coli-contaminated water, who might have been saved if the Walkerton Public Utilities Commission had admitted to contaminated water sooner, and about 2,500 became ill. An experimental drug in Phase III clinical trials, Synsorb Pk, was used to treat 19 children on compassionate grounds under Health Canada's Special Access Program.
During the time of the tragedy, both Stan and Frank Koebel denied any wrongdoing and firmly held that the water at Walkerton was safe to drink. However, as the tragedy grew in severity the two were eventually part of the criminal investigation into the tragedy, and, as a result, both would eventually plead guilty to a charge of common nuisance through a plea bargain. In their plea, they admitted to falsifying reports and Frank admitted to drinking on the job, as a beer fridge did exist at the facility.
They were both formally sentenced on December 21, 2004, with Stan receiving one year in jail and Frank Koebel nine months of house arrest. Reaction to their sentencing was mixed.
The Ontario Clean Water Agency was put in charge of the cleanup of Walkerton's water system.
An inquiry, known as the Walkerton Commission led by Court of Appeal for Ontario Associate Chief Justice Dennis O'Connor, reported in 2002. Part 1 was released in January 2002. It estimated that the Walkerton water tragedy cost a minimum of C$64.5-155 million and laid much of the blame at the door of the Walkerton Public Utilities Commission.
From the report:
The Walkerton Public Utilities Commission operators engaged in a host of improper operating practices, including failing to use adequate doses of chlorine, failing to monitor chlorine residuals daily, making false entries about residuals in daily operating records, and misstating the locations at which microbiological samples were taken. The operators knew that these practices were unacceptable and contrary to Ministry of Environment guidelines and directives.
The Ontario government was also blamed for not regulating water quality and not enforcing the guidelines that had been in place. The water testing had been privatized in 1996. CBC report)
Part 2 of the report made many recommendations for improving the quality of water and public health in Ontario. All of its recommendations have been accepted by succeeding governments of the province. The recommendations have also influenced provincial policies across Canada.
Key recommendations touched on source water protection as part of a comprehensive multi-barrier approach, the training and certification of operators, a quality management system for water suppliers, and more competent enforcement. In Ontario, these requirements have been incorporated into new legislation.
See also 
||This article needs additional citations for verification. (November 2010)|
- "August News and Events". Clinical Infectious Diseases 31 (2). 2000. Retrieved 1 June 2012.
- CBC News: Inside Walkerton Reference for the preceding three paragraphs: CBC News in Depth: Inside Walkerton
-  The Walkerton Report, Part One, described events in the community and a series of failures, both human and systemic, that led to contamination of the water supply. The report made recommendations based on the circumstances of the tragedy.
-  The Walkerton Report, Part Two, discussed water safety across the province and the steps needed to prevent similar tragedies. It made ninety-three recommendations.
- Contamination: The Poisonous Legacy of Ontario's Environmental Cutbacks.[dead link] History and context of the tragedy.
- Background article from the CBC
- Water Science and Technology article
- CBC Digital Archives - Death on tap: The poisoning of Walkerton
- The Walkerton Commission Reports
- Genetic Risk Markers for IBS Found in Walkerton Study, Toronto Star, January 28, 2010.
- Genetic Risk Factors for Post-Infectious Irritable Bowel Syndrome Following a Waterborne Outbreak of Gastroenteritis, Gastroenterology, Monday March 5, 2010.