Just 60 per cent of Christchurch's water supply will be reached by efforts to reduce chlorine levels following public backlash.

Five months after the city council revealed Christchurch's drinking water had been compromised it appears not a single well head has been fixed.

In January, councillors signed off chlorination of the city's water supply for 12 months while engineers fix vulnerable well heads.

The decision was made after Christchurch's secure bore status was revoked in December – a move prompted by the discovery that many wells were in disrepair and vulnerable to pollution from dirty surface groundwater.

Stuff has repeatedly asked the Christchurch City Council how many of the 102 well heads have been fixed, but it has refused to provide a direct response.

Asked how many well heads had been brought up to standard since work began, city services general manager David Adamson said: "Work is still under way on this."

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Nine wells at three pump stations had "been signed off as secure and are not being chlorinated", he said.

These were Keyes off Keyes Rd in New Brighton, Estuary off Estuary Rd in South New Brighton, and Prestons, near the corner of Prestons Rd and Te Korari St.

However, the nine wells were not included in the 102 needing work.

JOHN KIRK-ANDERSON/STUFF Council city services general manager David Adamson would not give a direct answer when asked how many of the compromised well heads had been brought up to standard.

In April, Stuff reported Christchurch Mayor Lianne Dalziel was adamant the city's water would be chlorine-free in a year.

But, asked whether the council was confident the water would be chlorine free in that timeframe, Adamson again failed to give a straight answer.

"As we have previously stated, the council has authorised the chlorination of the water supply for up to 12 months. Should longer be required, a further resolution of council would be needed," he said.

"Staff and our contractors are working to identify a range of options and strategies alongside the well head work that needs to be done so we can return to a non-chlorinated water supply as soon as possible.

"A report on this work is scheduled to go to council in the near future."

A date for the report had not been confirmed, he said.

Meanwhile, efforts to reduce the amount of chlorine in the water supply, following public outcry over the chemical's taste and smell, will affect 60 per cent of the supply.

The council had been pushed to lower doses after initially indicating residents were unlikely to taste the chlorine.

DAVID WALKER/STUFF People queue to fill containers at a fresh water spring on Ernlea Tce in Cashmere.

"As part of a range of things to help reduce the taste and smell, council contractors are flushing pipes in areas most affected by this," Adamson said.

"We are also working with the health authorities on other options to help reduce the smell and taste issues people are experiencing.

"Staff have received approval from the health authorities to reduce the amount of chlorine being added into the water supply in 27 pump stations.

"We are also looking at ways we can accelerate work on pump stations with mostly above-ground well heads to isolate the below-ground source and get approval to stop chlorinating those."

Sites where the chlorine dose was expected to be lowered were available on the council's website.

Adamson said it was "too early" to give the location of pump stations where work could be accelerated.

The council was also considering longer-term options.

"The council is looking at other options, such as to use ultra violet light or ozone treatment, where it might be appropriate, timely and cost-effective as an alternative to well-head upgrading," Adamson said.

"These solutions provide a similar level of protection to that of a secure wellhead. As each piece of work is completed and chlorine is switched off, we can manage the network so wherever possible we are using non-chlorinated water supply."