Upgrades will be carried out on several underground wells in Christchurch after an engineering assessment found that the wells could be susceptible to contamination.

The assessment, finalised in late-December, found that some wells may not be sufficiently sealed to prevent surface groundwater contamination - particularly in heavy rainfall.

Christchurch City Council has reassured the public the risk of contamination is minimal, though they are considering chlorinating the city's water supply while the wells are upgraded.

The chlorine would be in place to kill any bacteria that may get into the water.

Canterbury Medical Officer of Health Dr Alistair Humphrey says there's no current issue with the quality of the ground water - it is safe to drink.

"If you have a below ground bore that is not sealed properly, there are a number of ways contaminated water can egress into your groundwater," he said.

"If we have heavy flooding there is a risk some form of contamination could get into the groundwater, as it did in Havelock North."

In 2016 Havelock North saw an outbreak of a gastro illness when the local supply, sourced from shallow bores extracting groundwater, was contaminated.

While Christchurch's risk of water contamination is slight - the consequences of any contamination are potentially very serious so action needs to be taken, says council's head of three waters and waste John Mackie.

A boil issue notice for the city does not need to be in place.

Council has 156 wellheads across the city - 103 of those are below ground and all of those will be upgraded to meet standards.

The wells are inspected on a rolling basis by engineers to meet Drinking Water Standards and each well is reviewed at least once every five years.

- NZ Newswire