Walkerton and North Battleford--key lessons for public health professionals.

Since May of 2000, drinking water safety has achieved unprecedented publicity in Canada, yet we need to assure that we are all informed and not misled by media coverage. By now, public health practitioners in Canada must know, or at least may believe they know, the story of the Walkerton tragedy. * Fewer may be aware of the details of the North Battleford outbreak of April 2001. † What lessons should public health professionals derive from the findings of the major public inquiries into these Canadian outbreaks taken together with literature on other outbreaks in the developed world? First, the time-honoured framework for drinking water safety, the multi-barrier approach, is more relevant today than ever before. This approach, despite its diverse interpretation over time, offers the most effective framework for achieving drinking water safety. The Walkerton Inquiry Part 2 Report adopted it as the basis for developing a strategy for safe water. In addition to ensuring an effective regulatory process and a new commitment to total quality management, the multiple barrier approach was described as involving at least five main elements: • Source protection to keep the raw water as clean as possible to reduce the risk of contamination breaching the drinking water system; • Treatment, often involving more than one process, to remove or inactivate contaminants; • Distribution system security to protect against intrusion of contaminants and disinfectant residual use to assure delivery of safe water to consumers; • Monitoring programs to control treatment processes and detect contamination; • Responses to adverse conditions that are well conceived, thorough and effective. Multiple barriers are cost-effective because a risk reduction vs. cost curve for a single barrier is normally steepest (risk reduced per unit of cost) for the initial risk reduction, but will inevitably flatten out as we approach negligible risk. By placing suitably selected barriers in series to capture the steep risk reduction at lower cost for each barrier, a much lower cumulative risk can be achieved than by investing the same amount in a single barrier. How low we choose to push risk reduction is a choice that society must make by deciding how much we are willing to pay. For the purposes of this discussion, we will assume that Canadians do not expect to become ill or to die from drinking their tap water, so we should be committed to reducing risk to levels that are too small to worry about. The folly of placing our confidence entirely in a single barrier should be evident from exploring the Walkerton and North Battleford outbreaks. Although each involved interactions of many events and failures at more than one barrier, some aspects of these two outbreaks are revealing. Walkerton was a shallow groundwater supply that was supposed to be disinfected, but which failed to receive chlorination adequate to deal with pathogen contamination from cattle manure following heavy rains in May 2000. This failure occurred, in part, because the operators believed that the groundwater supply was a “safe” source and that chlorination was merely an unnecessary requirement that led to consumer complaints about taste. The operators’ faith in the safety of water from the shallow (5 to 8 m) aquifer at the infamous well #5 was woefully misplaced. In particular, a hydrogeologist’s report for the commissioning of this well, more than 20 years before the outbreak, confirmed that it was subject to surface contamination, required disinfection and recommended source protection that was never provided. North Battleford, in contrast, relied on a river water source (the North Saskatchewan River) that is subject to human and animal waste contamination and extreme turbidity (up to 1700 NTU) so that conventional treatment (coagulation, filtration and disinfection) is mandatory. But the total faith in this treatment at North Battleford was just as misguided as the total faith in the safety of source water at Walkerton. Poor performance of the community’s sewage treatment plant located upstream of the raw water intake for the drinking water plant had been tolerated as if the latter was failure proof. Excessive coliform levels in raw intake water had been noted dating back to 1963, and fecal coliform concentrations were reported as high as 150,000 per 100 mL in March 1993. When treatment processes for turbidity removal were allowed to become sub-optimal following process maintenance in late March 2001, the outbreak ensued in April. The media seized on the documented misdeeds of the inadequately trained operators at Walkerton. A functional multiple barrier approach applied with effective regulatory oversight would not have allowed their misdeeds to end in tragedy. In particular, Justice O’Connor found that effective implementation of continuous chlorine residual monitoring (an investment of ~$8,000), in accordance with policies for groundwater under the influence of surface Department of Public Health Sciences, University of Alberta Correspondence: Dr. Steve Hrudey, Department of Public Health Sciences, University of Alberta, Edmonton, AB T6G 2G3, Tel: 780-492-6807, Fax: 780-492-7800, E-mail: steve.hrudey@ualberta.ca