Wellington Water residual disinfection exemption application declined

The water services regulator Taumata Arowai recently declined a residual disinfection exemption application for Wellington Water’s Waterloo Drinking Water Treatment Plant (WTP).

Head of Regulatory, Steve Taylor said that the regulator had only one option given the clear requirements of the Water Services Act 2021.

“Our only option was to decline this application, because the supplier requested to be exempt from the chlorine contact time requirements,” said Mr Taylor.

Mr Taylor said that the chlorine contact time rule is critical to ensure that micro-organisms, like bacteria and viruses, are killed.

“As a part of primary treatment, chlorine needs to be in the water long enough to make it safe to drink,” said Mr Taylor.

Chlorine contact time is about making water safe as part of the primary treatment process. This is separate from residual disinfection, which is about keeping treated water safe after it leaves the drinking water treatment plant and moves through pipes before reaching people. The Water Services Act 2021 does not allow for residual disinfection exemptions for chlorine contact time.

The chlorine contact time rule isn’t new, it existed under previous Ministry of Health standards, as the former drinking water regulator. However, the minimum amount of contact time required to effectively disinfect water increased (from six to fifteen minutes) in November 2022. This adjustment was informed by expert, third party advice and followed consultation with the water services sector.

Wellington Water applied for an exemption for residual disinfection, although it was seeking to be exempt from chlorine contact time rules that only apply during primary treatment. This is why their exemption application had to be declined.

“While we consider there’s only a low risk posed to people in some locations near Waterloo WTP due to reduced chlorine contact time, their risk is slightly higher than it is for other people where the minimum chlorine contact time has been achieved,” said Mr Taylor. “So, we are pleased to see Wellington Water taking action through its programmed works to meet primary treatment requirements and ensure everyone they serve has access to the same, safe water.”

We are now talking with Wellington Water about its compliance options following this exemption application decision.

Read the final exemption decision paper. 

Media contact

• Email: media@taumataarowai.govt.nz
• Mobile: 021 367 937

Notes to editors

Additional information on chlorine and drinking water:

Chlorine is generally added to water during two separate stages of the drinking water treatment process.

First: Chlorine can be added to water that’s been collected from lakes, rivers, and aquifers in a drinking water treatment plant to disinfect it and help make it safe to drink. At this stage other equipment and processes may also be used to produce safe drinking water. In the water services sector, this is called primary treatment.

Second: Once water has been treated, it needs to be sent out to people – usually through pipes. Things like damage to drinking water pipes create an opportunity for bacteria and viruses to contaminate treated drinking water. So, a small amount of chlorine is also added when drinking water leaves the treatment plant to keep treated water safe as it travels from the treatment plant to people. In the water services sector, this is called residual disinfection.

For more information on chlorine and drinking water see: taumataarowai.govt.nz/chlorine

Additional information on the exemption process:

To grant an exemption from the requirement to use residual disinfection in a supply that includes reticulation, the water services regulator, Taumata Arowai, must be satisfied that the exemption is consistent with the main purpose of the Water Services Act 2021 - to ensure that safe drinking water is supplied to consumers. An application needs to demonstrate how the drinking water supplier will supply safe drinking water without the use of a residual disinfectant.

Taumata Arowai must also be satisfied that the drinking water supplied will comply with all other legislative requirements and the Drinking Water Safety Plan on an ongoing basis and that the exemption will give effect to Te Mana o te Wai to the extent that it applies.

Each supply is unique, and applications for residual disinfection exemptions are assessed individually on the information provided.

As part of the assessment process, Taumata Arowai provides information to applicants on what is needed to satisfy the requirements of the Act. Information on what is expected in an application is provided on our website - Guidance on applying for an exemption | Taumata Arowai