A boil water notice will remain in effect for close to 30,000 residents of northeast Hamilton and nearby rural communities until at least Tuesday, authorities say.
The notice was triggered on Saturday morning after a single water sample from the Rototuna reservoir tested positive for E. coli.
Follow-up testing at the reservoir and other sites across the city returned clear results, but standard safety procedure requires three days of clear results before the notice can be lifted.
Water should be boiled for at least one minute before it was used for drinking, cooking or preparing food, washing dishes, or brushing teeth.
An emergency mobile alert was sent to affected residents today.
Hamilton City Council three waters unit director Maire Porter said today's results were encouraging.
"We had a single confirmed test yesterday and immediately isolated the reservoir, supplied the zone from other areas of our network and commenced a network-wide testing and sampling regime. This is in addition to our routine testing programme."
The boil water notice applied to the Rototuna Water Supply Zone, which covered around 12,000 properties and 29,000 residents in the northeast of Hamilton, including the suburbs of Rototuna, Flagstaff, Huntington, and parts of Queenwood.
A small number of Waikato District residents in Gordonton and Puketaha were also affected as they were supplied by the Greenhill bulk supply point.
Full lists of affected streets were available on the Hamilton City Council and Waikato District Council websites.
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