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Nokia water supply contamination refers to the events on November 28–29, 2007, when large parts of the water supply in Nokia, Finland, were contaminated when sewage water (with solids removed) became mixed with fresh water. The contamination, affecting an area with some 12,000 inhabitants, caused an epidemic with thousands of cases of diarrhea and vomiting primarily due to Norovirus and Campylobacter infection. Hundreds of inhabitants were hospitalised and the town was forced to temporarily ban all use of water.
Contents
The cause for the contamination was revealed to be combination of different events. A maintenance man in the Nokia waterworks had opened a valve between fresh water and sewage water pipes to let some fresh water flush out the sewage pipe. The valve was installed against regulations. Because of pressure differences, the water flowed in the opposite direction, contaminating the fresh water supply. At the same time, at another site there was maintenance work done, and the first calls from people to tell the water was strange were dismissed as being connected to that event. Only after two days an official warning was given that the water is contaminated, and bottled water deliveries were started.
Background
In the Kullaanvuori water treatment facility, there was a poorly designed installation. A drinking water pipe was connected to a wastewater pipe for the purpose of flushing the wastewater pipe. Such an installation is illegal, and for a good reason, because if the water pressure in the drinking water pipe is too low, backflow occurs. This hazard was realized in the event. A maintenance worker accidentally opened the valve, and for two days, wastewater flowed into the drinking water supply. The contamination was actually detected, but the company decided to ignore it, assuming it was a transient pulse caused by the repairs.
Identified bacteria and viruses
As of December 15, 2007: