Risk Analysis of the Walkerton Drinking Water Crisis

This article helps explain why our drinking water is treated with chlorine after it is treated. Click here to read the full article or an excerpt below.


…One important purpose of the chlorine residual is to retain a capacity lot disinfection in treated water as it moves through the distribution system. Another objective is to provide a means to determine whether contamination is overwhelming the disinfectant capacity of the chlorine that has been added to the water. “The Walkerton operators did not manually monitor the chlorine residual levels at Well #5 during the critical period. Had they done so, it is very probable that they would have detected the fact that the chlorine residual had been overwhelmed” (O’Connor. 2002b, p14). In other words, the workers would have found that either the water was contaminated, or the chlorinator was not working, or both, and would have been able to take steps to protect public health. It is a relatively simple matter for a competent operator to correct the lack of chlorine residual, shut down the well, and alert the community to the problem. Although daiiy monitoring would not have prevented the outbreak, there is a high probability that it would have significantly reduced its scope. Instead, the contamination entered the system undetected (O’Connor, 2002c). The operators of the Walkerton water supply system did not intend to place public health at risk. Why did they neglect the chlorine residual? There were several reasons: the operators were sensitive to complaints from residents about excessive chlorine taste; they preferred the taste of the water before chlorination, and believed the water was safe (indeed, they often drank water at the well sites); and they lacked knowledge of E. coli bacteria. These attitudes were common among PUC employees for decades (O’Connor, 2002a,b).



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