Christchurch City Council will vote on a proposal which could see the tens of thousands of residents' water chlorinated.
The Council is considering chlorination at three pump stations which serve the city's northwest and have received a D-grade risk rating. The vote takes place on Thursday.
Canterbury medical officer of health Dr Alistair Humphrey says it's a case of better safe than sorry.
"Chlorination is one extra barrier that will reduce the risk of bacterial contamination of the water, such as capylobactor," he says.
"They're only chlorinating the bore - they're not putting the chlorine through the reticulation system, so most people won't notice it anyway."
It will only be a temporary measure with new wells which won't need chlorination expected to be in action by the end of March next year, Dr Humphrey says.
"It makes the water safer. We've seen what can happen when we have unsafe water, so making the water as safe as possible is a good idea."
The wells serve around 20,000 residents.
Mayor Lianne Dalziel believes the risk isn't too great, saying rigorous testing takes place on the water every day.