Water in the Hawea river probably contained more E-coli contamination than the town's water supply, even though routine testing of the water supply revealed a single count of the bacteria, the Wanaka Community Board was told on Tuesday.
Queenstown District mayor Clive Geddes addressed the board to allay concerns about contaminated drinking water supplies.
After flushing the Hawea reticulation system and water lines and further testing, the system was declared clear of contamination about January 19.
A high level of turbidity at the intake source was pinpointed as the cause.
Turbidity was the amount of suspended solids, such as silt, in the water, and when water was stirred up, the ultraviolet light treatment system did not always kill all bacteria, engineer Gerry Essenberg told the Otago Daily Times last week.
During discussion by the board, Mr Geddes said the council was required by law to issue boil water notices as soon as one part E-coli was detected, or treat the water with chlorine, which has been resisted at Lake Hawea.
It did not mean the system was not coping or had failed.
E-coli occurred naturally in waterways at a standard level of four parts, which was a much higher level than that found in the Lake Hawea supply, Mr Geddes said.
He agreed with board member Jude Battson it was reasonable for parents might worry about their children getting sick but he thought the risks at one part contamination were low.
"It is not as if you were to drink that water and come down with the stomach flu.
"You could get that from drinking from the Hawea River."
Mr Geddes said the council needed to make the context clearer when issuing media releases and boil water notices.
"We don't want a whole lot of alarm that drinking supplies are unsafe . . .
"If you go down and pick up water in a bucket from the Hawea River, it may have more E-coli," he said.
