Photo: AFP
Boil-water notices for several areas in Hamilton have been lifted.
The Rototuna reservoir tested positive for E. colia on Saturday, affecting about 30,000 residents and closing schools and businesses.
There had been no further positive E. coli test results since then.
Council Three Waters director Maire Porter said the city's water supply was safe to drink.
"The good news is that the boil notice has been lifted," she said.
This followed three days of E. coli testing.
Porter said council was now reviewing what might have caused the E. coli to enter the system.
"But right now there is no confirmed cause of the E. coli that we did detect."
But she said there was also no evidence of any breach of council's systems, either at the Rototuna reservoir or elsewhere on the system.
"Unfortunately, we may never know the exact cause."
Porter said it had been nearly 20 years since an incident like this in Hamilton and a need for such a large part of the community to boil their water was rare.
The last such case was when about 3500 properties were affected by a boil water notice in Dinsdale in 2006.
"We generally have a very high level of compliance, and we have very good systems in place," she said.
Porter thanked the community for their patience and understanding during the boil water period.
The council said businesses and residents needed to run all cold taps for five minutes, dispose of ice and refresh water in appliances before returning to normal water use. More information on these steps could be found on their website.
Steve Taylor, head of operations at New Zealand's Water Services Authority - Taumata Arowai, said Hamilton City Council did the right thing as a competent drinking water supplier.
"The council acted quickly, taking decisive action to protect public health and put the boil water notice in place," he said.
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