24 Aug 2016

The contamination of Havelock North’s water supply has raised questions about the safety of water supplies across the country.

Could Christchurch’s water supply be vulnerable to contamination?

We put some questions to John Mackie, who is Head of Three Waters and Waste at Christchurch City Council. Here is what he had to say:

How safe is Christchurch’s water supply?
In Christchurch we’re fortunate to have access to a reliable supply of high quality drinking water, most of which is sourced from underground. Most of our groundwater sources have achieved the highest possible rating for groundwater and is regularly monitored.

All of Christchurch’s groundwater sources apart from one are rated as being at very low risk of contamination. The Northwest Christchurch groundwater supply is not at the same level and the Council has plans in place to upgrade this source by June 2018. This source supplies about 80,000 people.

How often does the Council test the water?
The Council tests the water daily in large distribution areas in its accredited laboratory and less frequently in areas where smaller numbers are supplied. All secure groundwater sources and reservoirs are tested monthly. Water from shallow bores is tested more frequently (eg Burnside is tested daily).
The Council is not responsible for monitoring water quality in individual properties that collect rainwater in tanks or have their own private bores.

What about Banks Peninsula?
Many sites in Banks Peninsula, such as Akaroa and Little River, rely on surface water from streams for the Council-supplied water. These sources are treated with chlorine.

Is E.coli tested for?
Yes. E.coli is easy to detect and can be detected within a short amount of time, usually within 24 hours. The presence of E.coli is an indicator of faecal contamination of the water and means that other harmful pathogens could be present. Not all strains of E.coli are harmful to humans though; some are beneficial and naturally occur in the gut.

Has E-coli been detected in the water?
In the past year there have been nine incidents resulting in 14 positive tests for E. coli in the water from more than 5000 tests. This is much lower than the allowable limit.

What was done when the positive result was found?
When the contamination was discovered, health authorities were immediately notified, the source was isolated where possible, and measures taken to identify the cause and to treat the supply with chlorine or to flush the system. We also notified people in the affected areas who might have detected the presence of chlorine in the water.

Who oversees the testing regime?
The testing regime and frequency is approved by the Canterbury District Health Board’s Community and Public Health division. Information about positive test results and reports of illness to the Medical Officer of Health are matched to help identify issues as early as possible.

If water is found to be contaminated, do you have a plan for dealing with it?
We have a plan for how we would deal with any positive test for contamination, including immediately isolating the source while the contamination is confirmed and treated. The plan includes details on how we will get information out to the public as soon as possible.

What is the Council doing to maintain the quality of water supply?
The Council is in the process of upgrading bores in the Northwest of the city to deeper wells to reduce the risk of contamination. This work is on track to be completed by the end of the 2018 financial year.