Regional council votes to permanently chlorinate Lower Hutt drinking Water

  • Published Date 10 Aug 2017

Greater Wellington Regional Council has approved the permanent chlorination of Lower Hutt's drinking water. The Council voted in favour of a recommendation from Wellington Water, which has completed an investigation into the contamination of water supplied from the Waiwhetu Aquifer.

Wellington Water has completed multiple reviews, technical assessments, analysed incident reports, and sought advice from local health authorities and independent international experts about the change in water quality detected since September 2016. The most significant change is three detections of E.coli between December 2016 and April 2017.

The outcomes of these investigations were considered by the GWRC today.

Greater Wellington Chair Clr Chris Laidlaw says technical experts have provided a solid picture of the environmental and physical factors that could be influencing the aquifer, but there is no clear evidence of a single cause. Therefore decisive action is required.

"This is a complex area of study in an aquifer that is yet to be fully explored, and it's shown us there are no quick fixes to the issue of contamination. We can’t take chances when it comes to protecting public health, and that means continuing to chlorinate drinking water from the Waterloo Treatment Plant."

Wellington Water's review of the source of the changes at Waiwhetu Aquifer considered a broad range of scenarios, including the "shaking effects" of the Kaikoura earthquake, pathways into the aquifer via well-casings, and leaking stormwater and wastewater pipes.  Although these scenarios are considered unlikely to be the cause of the changes, they cannot be completely ruled out.

"We will continue to investigate the aquifer through a longer term study. This will improve our understanding, and ensure we have the right planning controls in place to protect the aquifer," says Clr Laidlaw.  

 Wellington Water took action to continue to provide safe and healthy drinking water to Hutt City customers in April 2017. The decision to continuously chlorinate the water supplied by the Waterloo Water Treatment Plant was taken as a precautionary measure in April in response to positive E. coli test results and a concerning increase in total coliforms.

Around the same time, a decision was also taken to install ultra-violet (UV) water treatment units to provide further protection against potentially harmful organisms in water supply. Wellington Water made these decisions in collaboration with GWRC and Hutt City Council, as well as Hutt Valley District Health Board’s Regional Public Health while investigations were completed.

Non-chlorinated drinking water will be available from fountains in Buick St and Dowse Square Lower Hutt. Drinking water at these fountains is now subject to filtration and UV treatment. Regional Public Health support the addition of UV treatment to the Buick Street and Dowse Square bores as a way of managing potential public health risk.

Lower Hutt Mayor Ray Wallace says no chances should ever be taken when it comes to drinking water quality.

"No one wants a repeat of the Havelock North experience. Public safety has always been our number one priority, and we must continue to listen to the experts who tell us that a combination of chlorination and UV treatment for our network is the best long-term approach.

"It's fantastic that we're also able to offer an unchlorinated solution in Lower Hutt for those that prefer it at the Buick Street and Dowse Square fountains. These fountains are now both open and treated with a UV filter and filtration. At the flow-rate of water from the fountains, the UV and filtration provides effective barriers against possible contaminants and means the water complies with the Drinking Water Standards of New Zealand.

"While it is sad that this has happened and investigations have not found a single root cause, it is something we must accept and I am confident that the best possible solution has been found for our city."

Background information

The Waiwhetu Aquifer can supply up to 70 per cent of the Wellington region's drinking water. Since September 2016 bacterial indicators in the aquifer have been recorded at concerning levels.

In response, Wellington Water introduced additional safety barriers and monitoring for Lower Hutt's water supply to safeguard against bacteria, viruses, or protozoa (such as cryptosporidium and giardia).

Wellington Water sought advice from independent experts on the results of investigations into the aquifer. The experts have advised that relying on the aquifer's natural filtration processes is unlikely to be sufficient to manage potential public health risk. The public health risks associated with an outbreak of waterborne bacteria have been well demonstrated in Havelock North.

As agreed with Regional Public Health, Lower Hutt's water supply was continuously chlorinated from April to ensure that the risk of potentially harmful organisms in water supply could be appropriately managed.

Wellington Water took all practical steps to continue to provide safe and healthy drinking water to Hutt City customers who received unchlorinated water prior to April 2017. As well as continuous chlorination, ultra-violet (UV) water treatment units will be installed at the Waterloo Water Treatment Plant. This will provide further protection against potentially harmful organisms in water supply.  Wellington Water made these decisions in collaboration with Greater Wellington Regional Council and Hutt City Council, as well as Hutt Valley District Health Board's Regional Public Health, whilst investigations were completed.

The Waterloo Treatment Plant commenced operating in 1981. It supplies drinking water to around 155,000 customers in Wellington and the Hutt City every day. Prior to April 2017, the drinking water for around 74,000 customers in Lower Hutt was sourced through the Waterloo Treatment Plant directly from eight bores connected to the Waiwhetu Aquifer, and was subject to minimal water treatment processes.

Wellington Water supplies an average of about 140 million litres of water every day for Upper Hutt, Lower Hutt, Porirua, and Wellington. With the exception of the 74,000 Lower Hutt customers, drinking water supplied to the rest of Hutt City, Wellington City, Porirua, and Upper Hutt has been chlorinated since 1981.

Chlorine is highly effective at killing harmful bacteria that may exist in the water or in the water supply pipes. It is added to safeguard the water from bacteria, and to ensure the water supplied from the Waterloo Treatment Plant complies with the Drinking Water Standards for New Zealand.

Local authorities have certain obligations under the Health Act regarding the supply of safe drinking water - GWRC are the designated water supplier, and Hutt, Porirua, Upper Hutt, and Wellington city councils own the local distribution networks. Wellington Water works on behalf of all five councils, to manage and monitor the region's drinking water supply.  Regional Public Health provides oversight and approval of the work of the councils to maintain a safe water supply that meets New Zealand Drinking Water Standards.

Full information is available on the Wellington Water website:



Updated April 28, 2022 at 2:40 PM

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