Authorities have found 22 sewage treatment plants that use the same kind of valve that caused massive water contamination in the town of Nokia.
Theses types of valves - which should not exist anymore - could theoretically allow sewage into the drinking water supply. A maintenance worker accidentally opened one of these valves in Nokia last November, causing drinking water to be tainted with sewage.
YLE's investigative show A-Studio reports that one of the valves connecting clean and untreated water was discovered in the water treatment facilities of a major food producer.
After the disaster in Nokia, the Ministry of Social Affairs and Health launched a probe to discover if more of these valves existed.
The residents of Nokia had to make do for weeks without using tap water, even for showers, washing machines, and dish washers. For two months afterwards, many areas were instructed to boil tap water before use. The entire area has just recently been given the all-clear.