Councils around the North Island are assuring residents of the safety of their water supplies following a gastro outbreak in Hawke's Bay.

Water quality has been in the spotlight after about 4100 were struck down with a gastro illness caused by campylobacter from a contaminated Havelock North water supply.

A water tanker filled in Hastings to help deal with the crisis had a positive indicator of e-coli yesterday but has since returned a clear test.

Watercare treats Auckland's water to comply with the Drinking-water Standards for New Zealand 2005, according to Watercare Services media liaison Pippa Curd.

She said the company had thorough risk management practices in place and quality assurance systems that enabled the company to supply Aa graded water to its customers across the Auckland region.


"This means that there is an extremely low level of risk associated with the operation of the water supply."

Curd said e-coli was an indicator of faecal matter being present in the water and could be used as a comprehensive indicator of the presence of similar bacteria, including campylobacter, in water.

In the year to the end of June, the company carried out 8917 routine water sample tests for e-coli and it was not detected in any of the samples.

Curd said Watercare used chlorination to prevent the passage of potentially harmful microorganisms to Auckland's drinking water.

Hamilton City Council compliance manager Trent Fowles said e-coli didn't show up in any test results for Hamilton City Council's water supply last year.

"We have an extensive testing programme which exceeds the NZ drinking-water standards in all areas of the city."

In all, the council undertook 790 tests for e-coli last year.

Otorohanga District Council chief executive Dave Clibbery said there were no instances of e-coli in Otorohanga's water supplies last year or in other recent years.

The town supply was tested about twice a week and other small supplies were tested every 10 days. It conducted 325 tests for e-coli per year across all the water supplies in the district.

Clibbery said water on all supplies other than an extremely small agricultural supply were continuously disinfected with chlorine, unlike in Havelock North.

Taupo District Council communications manager Lisa Nairne said all 19 of the district's water supplies were chlorinated and 17 of those were subject to continuous monitoring.

No e-coli was detected in council supplies last year in the 905 samples tested, she said.

The Kaipara District Council said there was no e-coli detected in its supplies last year.

Communications manager Helen Slater said supplies were tested once a week.

Far North District Council senior communications advisor Ken Lewis said all treated water supplied by the Far North District Council was treated with chlorine.

The design of its plants meant that if water leaving the plant did not receive sufficient chlorine dosing, the plant would close down and an alarm would alert the operator.

Council test for e-coli 1140 times in the Far North last year, said Mr Lewis.

Waitomo District Council communications officer Kelly Marriott said council also had no positive e-coli detections last year.

Water supplies were tested weekly and chlorine tests were carried out twice a week.

No e-coli was detected in Waipa District Council's water supply in the last year either, according to a council spokeswoman.

Matamata-Piako District Council utilities team leader Dave Locke said council had a contract with an independent laboratory to test the water between every five and 11 days depending on the population and water source.

Between 800 and 900 independent tests were carried out last year as well as other internal testing. E-coli wasn't detected the water at all last year.

E coli has not been detected in any water supply across the Waikato district in the past year, according to Waikato District Council general manager Tim Harty.

About 652 samples were taken during around 84 checks each year, he said.

Hauraki District Council spokeswoman Paula Trubshaw said the potential presence of e-coli had been detected the district's water supply four times since 2013.

Three of those cases tested negative in subsequent, more comprehensive tests carried out the same day results were received. One continued to show the potential presence of e-coli. On this occasion a chlorine dosing fault was discovered and repaired, a boil water notice was issued to residents, and the network was flushed until chlorine levels were sufficient to ensure e-coli could not survive in any part of the network.

Trubshaw said a mixture of tests were applied throughout the district including chlorine testing.

South Waikato District Council communications manager Kerry Fabrie said council tested water supplies every four days at Waihou and every eight days at all other sites.

It tested 697 samples in water reticulation last year with just one false positive.