The boil water notice affecting thousands of residents in Christchurch’s eastern suburbs has been lifted after the source of contamination was narrowed down to a small section of pipe serving about 20 homes.

Christchurch Mayor Phil Mauger said routine weekly testing on Saturday detected a high reading, prompting the council to issue a precautionary boil water notice across the wider Rawhiti zone.

“You’ve got to do it,” Mauger said. “If you don’t and someone gets sick, all hell will break loose.”

The notice affected parts of New Brighton, Burwood, Wainoni, Aranui and Southshore.

After further sampling, council teams were able to isolate the issue to a submain pipe feeding around 20 properties near a testing point.

“It’s only a submain, not a main on the road, and it feeds about 20 houses,” Mauger said. “We’ve isolated that little bit and talked to the 20 people in those houses and they’re more than happy to boil their water until we get it sorted.”

He said the rest of the zone had now returned clear results and residents outside the isolated area no longer needed to boil their water.

Investigations are continuing, but Mauger said early indications suggest the contamination may be linked to recent work on the network, possibly something as minor as a water meter replacement.

“It’s not E. coli, it’s not the wells, it’s not the pumping station,” he said. “There’s a bit of dirt somewhere along the line that’s got in there and the testing regime has picked it up.”

Mauger described the council’s testing programme as highly sensitive. “If you’ve got the tiniest bit of something in there, it’ll notice it,” he said.

He said the council required three consecutive clear days of sampling to ensure the problem had resolved before lifting the notice for most residents.

“It’s just to make sure that whatever was a problem has cleared itself up,” Mauger said.

It was not  linked to the Bromley Wastewater Treatment Plant ponds. “Nothing at all. Nothing whatsoever,” he said.

Turning to concerns about odour from the Bromley ponds, Mauger said conditions had improved, with previously red rated ponds now sitting at orange.

“We’re keeping an eye on this rain to see how much is going to come through and how that will affect it,” he said.

With heavy rain forecast, he said the council was better prepared than during previous events.

“We’re on top of it. The damn sight more than we were last time,” Mauger said.

While apologising to residents who had to boil their water, Mauger defended the decision to issue the notice.

“I know it’s disastrous for the people that had to boil their water and I’m very sorry for that,” he said. “But if we didn’t do it and there was a problem and people got sick, we’d be in the gun big time.”