An apparent E. coli failure on a rural water scheme near Lawrence had authorities in South Otago scratching their heads last week.
A Fulton Hogan contractor sampling water believed to be from the Evans Flat pumping station on the Tuapeka West scheme last month detected low residual chlorine in the supply.
At a council meeting on Thursday, Clutha District Council group manager service delivery Jules Witt said, in accordance with protocol, this had triggered a standard E. coli test procedure carried out by the contractor and associated laboratory Citilab, in Dunedin, over three consecutive days.
However, in an unexplained "oversight'', neither Fulton Hogan nor Citilab immediately reported the failure to the council.
Furthermore, it appeared the original sample collected had not been processed within the standard 24 hours required, possibly leading to a false positive result.
Subsequent testing for E. coli yielded negative results.
Had E. coli been present, consequences for the 283 users of the scheme could have been severe, Mr Witt said, and would have led to a "boil water'' notice.
Inquiries by Fulton Hogan and the laboratory late last week found human error was to blame for the confusion.
"Fulton Hogan also performed a private sample analysis for a customer named Evans at around the same time [as the Evans Flat analysis] which was positive for E. coli.
"The Fulton Hogan report then accidentally included reference to private customer Evans as a failed result for our Evans Flat water source.''
Other than the naming error, protocol was followed and there was no risk for Tuapeka West scheme users, Mr Witt said.
"From a public health perspective it's good news, but this false alarm has reinforced to the contractor they need to be particularly vigilant regarding water test results, and we will work with them to review future procedure.''
Mr Witt said capital upgrade works of $950,000 were planned for Evans Flat, which would support the continued provision of consistent water quality in future.
