Questions
1. State the quality characteristics of drinking water.
2. Draw a process flow diagram for water treatment of a town like Walkerton that vises well water.
3. Apply the HACC'P analysis to develop a quality' management system for water treatment of such a town.
In May 2000, seven residents of Walkerton, a small town in southern Ontario, died of E. coli poisoning transmitted through the town’s water. The water had been drawn from a well that was visually a safe source of water supply. Although well water treatment was rather simple—just added chlorine to disinfect it—tire town water works5 manager, Stan Koebel, believed that the water was so safe that chlorine did not have to be used.
This conclusion may have been true under normal circum-stances; however, during April 2000 the farm adjacent to the well fertilized its fields with cattle manure. Unfortunately, during the second week of May, the area received unusually high levels of rain, which washed E. coli from tire manure into the well. The usual level of chlorine was inadequate to kill the high level of the bacteria. Compounding this, Koebel did not follow the Ontario Ministry of the Environment’s guideline for checking the level of residual chlorine in treated water (in fact a minimum of .5 mg per litre should remain to continue disinfecting the water through the distribution pipes).
During the third week of May, people started to get sick. Water was finally tested and E. coli was found in the samples. Koebel kept quiet for a few days, hoping the nightmare would end. Unfortunately, the situation got worse: almost half the town’s population got sick and eventually seven people died.