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Published 7/03/2023

Drinking water rules change, water remains safe to drink

New rules introduced by Taumata Arowai, the national water services regulator, late last year mean the Waterloo Treatment Plant no longer complies with chlorine rules.  The change impacts up to 800 Lower Hutt households.

“It is important to note that the water being supplied from the Waterloo Water Treatment Plant is still safe to drink,” says Tonia Haskell, Wellington Water’s Acting Chief Executive.  “The plant was compliant under previous rules, and it is only recently when the rules changed, that it stopped meeting the chlorine rules.”

The new rules now require water suppliers to increase a value known as a ‘Ct’, determined from the amount of chlorine added to drinking water and the time that it must spend in contact with the water before reaching consumers, to further reduce the risk of bacteria. Chlorine guards against the risk of treated water becoming contaminated within the supply network as it flows from the treatment plant to households and is a precaution against the slim possibility of contaminants getting through the treatment process.

Waterloo Water Treatment Plant supplies drinking water to most of Lower Hutt and parts of Wellington City, however only certain households in Lower Hutt are impacted.

“We estimate that at any given time, depending on supply and demand levels, potentially up to 800 households in Epuni and Fairfield in Lower Hutt, are impacted by this. 

“We are continuing with our regular monitoring of the drinking water from the bores supplied from the Waiwhetu aquifer, as well as at the Waterloo Water Treatment Plant and locations within the drinking water network, to ensure that the drinking water continues to be safe. The results show there are no E.coli or any other potentially disease-causing organisms in the water. This is true of all the treatment plants Wellington Water operates on behalf of councils in the region.

“Meeting the new rule means either significantly increasing the concentration of chlorine added at the treatment plant or increasing the time that the chlorine is in contact with the water before it reaches the first customers in Lower Hutt. Increasing the chlorine concentration to this level, which is around two and a half times the current dose, could result in a significant change to the taste of the water or cause skin irritation. Alternatively, significant network upgrades and investment are needed to increase the contact time between chlorine and water,” says Tonia.

“We are working with our council owners and the regulator on this issue and the best way forward. In the meantime, Wellington Water has completed an independent technical study which has reaffirmed to us that the current treatment process is effective. We have submitted this to Taumata Arowai and have asked them for an exemption until we can complete the upgrades needed to meet the new requirement. We are awaiting the regulator’s decision.”

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