Extreme weather due to climate change is going to put more pressure on drinking water infrastructure, leading to more boil notices and e-coli scares, says a public health professor.

Photo: RNZ / Rebekah Parsons-King

Napier, Levin and Lower Hutt have all had recent threats to the quality of drinking water, while a government inquiry into the Havelock North water crisis last year continues.

The Horowhenua District Council has again had to issue a precautionary boil notice to residents of Levin after overnight rain brought mud and debris from slips into the Ohau River.

A boil notice was issued on 3 February, but was revoked during the weekend.

The Ohau River supplied the council's treatment plant, which treated it before it was made available to Levin residents to use.

Photo: Supplied

Water services manager Paul Gaydon said the murkiness of the water was too high and Levin has had to resort to its backup water supply.

"We've monitored the turbidity of the Ohau through the morning and it's gone up steeply.

"We're hoping it will come down just as quickly but we've had to stop production and it's still stopped.

He said people needed to be careful with their water use.

"It's serious, you know. We have some water on hand in the reservoirs but we need people to be very careful and very aware that we're in quite a difficult situation."

In Napier the reservoir tank that tested positive for e-coli last week has been given the all-clear after three consecutive negative tests.

The Napier City Council started to treat the Enfield Road reservoir with chlorine last Thursday after two positive e-coli readings.

Council spokesperson Chris Dolley said that reservoir was still only partly back in operation and residents should still be careful about water use.

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"We have decided the safest course of action is to continue chlorinating for the next three to four days while we have the reservoir cleaned by a team of divers.

"This will remove any doubt about what was the potential contaminant for this reservoir," Mr Dolley said.

Wellington Water said it expected a third consecutive negative test for e-coli to come in this evening after testing 21 water sites in Lower Hutt.

More issues around drinking water supply were likely to surface, according to Michael Baker.

A public health professor at the University of Otago in Wellington, Dr Baker said climate change would mean extreme weather, such as floods and heavy rain, would continue to test infrastructure protecting drinking water.

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"Extreme weather events put huge stress on a number of systems, particularly drinking water supply systems.

"That's because of flooding events, which can overwhelm normal treatment facilities, but also they can knock out power supplies and back up systems.

But Dr Baker said the jury was still out as to whether there was an increase of cases where drinking water had been jeopardised.

"There's obviously heightened awareness about water contamination at the moment.

"You really have to take a long term perspective and look at data on waterborne disease outbreaks and levels of contamination."

Hastings District Council mayor Lawrence Yule agreed with Dr Baker that more adverse weather events were going to challenge drinking water infrastructure.

He said an inquiry looking into the Havelock North water crisis may raise questions about the government's specified drinking water standards, which were last revised in 2008.

"Even in the Havelock North case the testing was being done more than was required by the New Zealand drinking water standards, yet a whole lot people still got sick.

"So I think that the inquiry will look at that and I expect there will be some changes recommended as part of that."

Mr Yule, who was also the president of Local Government New Zealand expected there would also be stronger rules on land use near drinking supplies to minimise the level of contamination from animals.