Council ends Hamilton boil water alert following E. Coli contamination probe

The council issued public alerts at 4.30pm on Saturday after discussing the findings with the water services regulator, Taumata Arowai. Photo / John Borren

Hamilton City Council says the cause of the E. coli contamination that led to last week’s city-wide boil water notice may never be known.

E. coli was detected in a routine sample taken from the Rototuna Reservoir at 2.30pm on Friday, October 3.

Preliminary results came through the next morning.

After consulting water regulator Taumata Arowai, the council issued public alerts at 4.30pm on Saturday.

Three Waters Unit director Maire Porter said the exact cause may never be known.

“Even in a modern, well-resourced water network like Hamilton’s, contamination can still occur due to unexpected events,” she said.

Council staff inspected the reservoir, checked treatment and quality data, and carried out physical inspections.

They found nothing unusual.

The council increased testing across the network, taking samples from more than 120 sites over three days.

All results came back clear of E. coli.

The irregularity was traced to a single sampling site, not the wider water system.

Officials lifted the boil water notice shortly after noon on Tuesday, October 7, after three consecutive days of clear results.

During the alert, the council worked closely with the Ministry of Health to support aged-care facilities and residents with specific health needs.

Schools and childcare centres closed or adapted operations depending on access to safe water.

Porter said the incident proved that Hamilton’s monitoring and response systems worked as intended.

“This should give the public confidence in our systems, our knowledge, and our capability,” she said.

The council said it would continue enhanced monitoring in Rototuna over the coming weeks before returning to regular testing schedules.

Routine testing includes weekly E. coli sampling and continuous monitoring of chlorine and pH.

The Rototuna Reservoir, opened in 2017, had no recent works linked to the contamination.

The council managed the response, extra testing, and public communication within existing budgets.

Porter said lessons from the incident would help improve future monitoring, alert systems, and public communication.

The council did not plan any immediate infrastructure changes.

Hamilton’s water remained among the highest quality in New Zealand, Porter said.

Porter said incidents like this could happen from time to time but she stressed the importance of being ready.

“The key thing is that we have systems in place to respond quickly and effectively,” she said.

She encouraged residents to stay prepared for emergencies by keeping at least three days’ supply of food and water on hand.

Tom Eley is a multimedia journalist at the Waikato Herald. He previously worked for the Weekend Sun and Sunlive.