Last Sunday marked the 10 year anniversary of the E. coli outbreak that was caused by contamination of the water supply in Walkerton, Ontario. In May of 2000, more than half of the town’s 5,000 residents became severely sick and seven people died as a result of bacteria laden water.

The drinking water supply became tainted when cow manure washed into a well that was vulnerable to contamination. The tragedy might have been prevented if animal access had been restricted in the watershed. To make matters worse, however, officials at the Walkerton Public Utilities Commission had received E.coli bacteria test results that showed unsafe levels of contamination, but concealed them for a number of days before finally alerting the public to the unsafe water.

An independent commission reported that operators at the Walkerton Public Utilities Commission had engaged in a host of improper operating practices for years, 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 report made recommendations for improving the quality of water and public health that have been accepted by succeeding governments of Ontario and have also influenced provincial policies across Canada.

Most U.S. water systems employ chlorine-based disinfectants to achieve lasting residual protection from waterborne disease throughout the distribution system as this is mandated by the Safe Drinking Water Act. The Walkerton anniversary serves as a reminder and illustrates the importance of watershed protection and diligent monitoring of chlorine levels by water treatment officials.

For more information about the safety benefits of chlorinated water, please visit our website.

And for more information about the Walkerton crisis, please visit my blog.

(Joan Rose, PhD, is the Homer Nowlin Chair in Water Research at Michigan State University and a member of the Water Quality & Health Council.)

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