Date set for chlorination of city water

Christchurch’s water supply will be chlorinated from March 26, starting with Brooklands, Kainga and Heathcote Valley.

A decision to treat the city’s water supply while engineers fix vulnerable well heads was made in January after Christchurch’s secure bore status was revoked in December, a move prompted by the discovery that many wells are in disrepair and vulnerable to pollution from dirty surface groundwater.

Councillors voted to temporarily treat water at the city’s 56 pumping stations. Supplies will be sterilised with chlorine for up to a year to stave off potential contamination.

The first widespread treatment of Christchurch’s drinking water since the 2011 earthquake, the chlorination programme will take about four weeks to be rolled out across the city, starting in the Brooklands, Kainga and Heathcote Valley areas.

Christchurch City Council city services manager David Adamson said it was not possible to say exactly when chlorination would begin in individual suburbs.

Leaflets will be put in letterboxes to let people know when they should expect work to start in their area.

Chlorination is required only at water sources, so treatment is not needed throughout the entire supply network.

Meanwhile, the council has announced Bruce Robertson, a former assistant auditor-general and director of Audit NZ, will lead an external independent review into the future of Christchurch’s unchlorinated water supply.

The review will examine both how the city reached the point where treatment was necessary and what would need to happen for it to qualify for any possible exemption from the mandatory treatment of supplies that was recommended in the Havelock North report.

Robertson was involved in reviewing Hastings District Council’s water service operations after the Havelock North contamination.

Adamson said Engineers will inject water with chlorine at the pumping stations and then check it further along the network to ensure it has mixed properly and they have the dosage right.

‘‘We are putting in a very small dosage,’’ he said.

Adamson said chlorinating at the source of the problem would reduce the likelihood of smell or taste issues.

Chlorine may be noticeable, but in most cases any effects were likely to be diluted quickly as the chlorinated water mixed with fresh, untreated water.

‘‘The chlorine reacts with organic matter and that creates products that you will taste. If you taste chlorine, it means it’s doing its job – it’s reacted with organic matter.’’

He said authorities would, in their ‘‘best endeavours’’, ensure work was carried out within the expected 12-month timeframe, though that could be shorter in some areas as wells were gradually made safe.

The council faces a substantial bill to repair the well heads. It was originally thought 28 wells required work, costing $840,000, but 103 have been found to be substandard.

Engineers were still assessing the viability of many well heads so the final bill remained some way off.

"If you taste chlorine, it means it's doing its job."

Council city services manager David Adamson