Christchurch City Council staff are rushing to find another way to get chlorine out of the city's water within its 12-month deadline.
The council controversially voted for chlorination in January after it was discovered some of the city's 156 wells were at risk of contamination during flooding.
At the time it was the only major city in New Zealand not to treat its water in that way, and the council promised chlorination would last only a year.
A council report, just released, said there was not enough time to bring some of the wells up to best practice, which involved raising them above ground, and remove chlorine within the timeframe.
They say staff were doing more work with contractors to see if the timeline can be brought forward.
Water Supply programme manager Helen Beaumont said other options were being considered.
"What we have done is mapped out a programme for the full remediation works ... and we can't do that within the timeframe."
"Now, we are looking at the alternatives."
These included fixing below-ground well heads to current - but potentially not future - standards or rolling out more UV treatment.
That one year deadline was still the target, even if the council could not do what it initially wanted to do, Ms Beaumont said.
"We are having to look at more than one way of getting there," she said.
The report is expected to be discussed on Thursday.