As the third case of Guillain-Barre Syndrome has been linked to the Campylobacter contamination of Havelock North’s water supply, New Zealand, chlorinating water in Christchurch’s northwest is off the table, for now.

The Christchurch City Council went against its own staff advice and unanimously decided on Thursday not to consider temporarily chlorinating the water from eight shallow wells that feed into three pump stations, serving about 20,000 residents.

The council instead decided to accelerate a $16 million programme to replace 22 shallow bores, supplying 80,000 northwest households.

The work was originally due to be finished by June 30, 2018, but most of the wells would now be decommissioned by March 2017. Fourteen of the most vulnerable shallow wells have already either been decommissioned or shut down.

Accelerating the work would cost an additional $480,000.

The council would also embark on a programme to raise community awareness of the risks of drinking untreated water from the shallow bores.

Canterbury’s medical officer of health, Alistair Humphrey, last month asked the council to explain why its continued use of the shallow wells did not present “an untenable risk”. Humphrey’s request was prompted by a gastro outbreak caused by campylobacter in the water supplying the town of Havelock North in Hawke’s Bay.

Staff will now talk to Humphrey to see if he was satisfied with the council’s response, without chlorinating the water. They will report back to the council in November.

Water from the bores was tested for E.coli daily, but it took at least 24 hours to get the results, so there was always a 24-hour period where contamination could go undetected, council three waters and waste boss John Mackie said.

He said the council complied with the water standards, but his professional advice to the council was to chlorinate the water, which would eliminate the risk.

Mayor Lianne Dalziel asked Mackie if the risk from the shallow bores had changed in the last few years. He said no.

She said it was only the perception of risk that had been heightened since the Havelock North contamination.