A $4.8m project to improve drinking water quality in north-west Christchurch could be sped up in the wake of the Havelock North gastro outbreak.

Due to the lower water-quality grading, the city council is renewing the bores that supply water to about 80,000 people. It is meant to be completed by June 2018.

However, city councillors are calling for the process to be accelerated to reduce the risk of drinking water contamination.

"Given the increased national attention in this matter, councillors want to understand how we could reduce risk even further than the level it is now," city council head of three waters and waste John Mackie said.

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He said no date had been set for a decision on whether it would be accelerated.

Most of the city's groundwater is graded Ba - the highest possible grading for an untreated secure groundwater supply.

However, the groundwater supply to the north-west is rated Da - unsatisfactory level of risk - because the area is served from shallow aquifers.

The city council programme would see the shallow bores renewed to improve water quality.

So far, new bore holes had been drilled, but the head works, pumping and electrical work needed to be done, Mr Mackie said.

An outbreak of campylobacter bacteria in Havelock North's water supply caused about 4700 people to get sick. Mr Mackie said the city council had already increased its sampling of shallow bores in the wake of the contamination.