Why didn't the water-treatment and monitoring system work?

It takes a formal provincial inquiry to answer this question. It is a puzzle; as far as investigators know, there has never been a major E. coli outbreak spread through a modern, chlorinated water system.

The inquiry reveals a whole series of circumstances that contributed to the failure to decontaminate the water supply promptly. You can read the full report.

The inquiry discovers, among other things, that:

  • Well 5, according to regulations, should have been fitted with a continuous chlorine-and-turbidity monitor, but was not. If it had been, the contamination would have been noticed almost immediately and the town's water could have been supplied from its other two (uncontaminated) wells.
  • The water-system manager and staff are poorly trained. Some of them do not understand basic principles, such as the need to keep a certain level of residual (extra) chlorine in the water, so that any sudden influx of contaminants can be dealt with. They also do not understand that Well 5 is vulnerable to contamination from run-off after heavy rain, and that E. coli O157:H7 can cause death and long-term disability.
  • For years, water-system operators have not been operating the system properly. They seem to have believed that the town's water supply was perfectly safe, have often drunk untreated water from the wells, and have not treated the process of water purification as a serious responsibility. The inquiry reveals that operators frequently have not added sufficient chlorine to the water, have failed to monitor chlorine levels daily as required by law, and have even falsified the testing records.
  • When the province quit testing municipal water itself and turned the job over to private contractors, it neglected to set up regulations requiring the private labs to notify the province or public health authorities when they detected contaminated water.
  • This has made it possible for the manager of the water supply to cover up what has been going on. Before people had begun to show any symptoms of illness, the manager had, in fact, received reports from the lab indicating that Walkerton's water was contaminated with E. coli. He not only failed to act on these reports, but kept them secret during the first days of the Health Unit investigation.