Christchurch City Council is starting to lower the amount of chlorine it is putting in the water at some of the city’s pump stations in an attempt to address taste and smell issues.

“We have already been given approval by the Drinking Water Assessor to reduce the dose of chlorine at 27 of the 53 pump stations that are being treated,’’ says Council General Manager City Services David Adamson.

This will reduce the overall concentration of chlorine in the drinking water.

“We are hoping reducing the dose will help with the taste and smell issues that some people have been experiencing but until we roll this out we cannot make promises.

“The advice we have had from our independent expert suggests the lower dose could reduce the taste and smell issues, but there is a chance it may not make a significant difference.

"That being said, both our expert and the Drinking Water Assessor believe the potential benefits outweigh that risk and it is worth shifting to a lower dose where we can,'' Mr Adamson says.

The 27 pump stations where the Council will be lowering dose have been selected because they are in areas where the water travels down the pipes for at least two minutes before reaching people’s homes.

That two minute lag is important because it allows enough time for the chlorine to be effective at a lower dose.

At the other pump stations the chlorine only has a minute’s contact time with the water before people start drawing on it so the dose needs to remain at current levels, until alternative measures can be put in place.

"There is some work to be done at each of the affected pump stations in order to change the dose so the lower dosage will be rolled out progressively over the next couple of weeks. We'll be updating our online map(external link) to indicate the dose rate at each pump station.

“We will be closely monitoring the impact of reducing the chlorine dosage and will continue to have ongoing discussions with the Drinking Water Assessor about how we can reduce the amount of chlorine in the network,’’ Mr Adamson says.

“This week we will also be continuing the work we are doing to flush the pipes with high pressure water in the suburbs that seem to be noticing the taste and smell of chlorine the most. Hopefully that too will help reduce the short-term taste and smell issues.

“Longer term we are looking at a range of options including treating the water with ultra-violet or ozone. We are prioritizing our well head improvement work on those pump stations where we are most likely to get approval to stop chlorinating. We are also looking at water demand and the way we use the network so that we can provide as many people as possible with unchlorinated water,’’ Mr Adamson says.

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