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The most alarming lead contamination results from the testing of East Otago water probably had different causes, an exhaustive investigation has found.
Lead in sediment or material from the sample tap was the likely cause of a high reading at the Waikouaiti raw water reservoir in January.
High readings at the Waikouaiti Golf Club and Karitane Bowling Club in December last year were probably caused by lead leaching from pipes and fittings.
The Dunedin City Council concluded there was no widespread lead in its drinking water network.
Residents of Waikouaiti, Karitane and Hawksbury Village were told on Wednesday they could resume drinking tap water after a six-month break because of the lead scare.
An investigation into why elevated levels of lead had been detected between July last year and January this year focused on two dates — December 8, 2020, and January 20, 2021.
Localised lead leaching from pipes and fittings was the most likely cause and changes in water chemistry may have affected the results that day, the investigation team found.
Stagnation of water was considered a likely factor.
Lead was regularly detected from the golf club tap, but not from the nearby distribution main.
Public Health South recommended people do not drink the water at the golf club and suggested pipe work there would probably fix the problem.
Readings at the bowls club appeared to result from an old meter and it had since been replaced.
The other alarming result was from the Waikouaiti raw water reservoir on January 20, implying a problem might be present at the water source.
Lead is present at trace levels in Waikouaiti River sediment and the water treatment plant removes such particles.
A sharp spike in turbidity, or cloudiness, was recorded at the raw water reservoir on January 20 and it was running at a low level at the time.
Corrosion of a tap may also have been relevant.
The city council is confident there is no E. coli in the water.
The most likely cause of an unusual E. coli reading at Karitane this month was contamination of the water sample.