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Waikato District Council - Te Kaunihera aa Takiwaa o Waikato

Water supply and arsenic

Arsenic level in treated water supply meeting Drinking Water Standards

Updated 12.54pm, 2 December 2024.

An arsenic reading of 0.010mg/litre was confirmed this morning from Ngaaruwaahia water treatment plant, meeting the 0.010 mg/litre maximum acceptable value (MAV) under Drinking Water Standards.

Results from the Te Kauwhata plant show a reading of 0.0026 mg/litre, and the level from Huntly water treatment plant is 0.0075 mg/litre.

Watercare Waikato is adjusting treatment process slightly at the Ngaaruawaahia plant, by introducing chlorine at the front end of the process to optimise existing arsenic removal processes.

The arsenic level in treated water supplied to our residents in Tuakau and Pookeno also remains within the MAV set by Drinking Water Standards.

Latest results available show treated water supplied to residents in the Tamahere/Woodlands Ward from Hamilton City Council still has slightly elevated levels of arsenic  - but, the water is still safe to drink.

Arsenic is a naturally occurring heavy metal found in the Waikato River. Some of it comes from the geothermal activity near Lake Taupo and other natural sources downstream.

Treated water will continue to be tested daily over the next few days.

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FAQs

What do the test results show?

Recent test results received on 25 November from Watercare’s water treatment plant near Tuakau showed a slightly elevated reading for arsenic in the treated water supply. 

The ‘maximum acceptable value’ under NZ Drinking Water Standards for arsenic in New Zealand is 0.01milligrams per litre.

Watercare reported a result to national water regulator Taumata Arowai of 0.011 milligrams per litre.

Why have increased arsenic levels been detected in drinking water?

Arsenic is a naturally occurring heavy metal found in the Waikato River. Some of it comes from the geothermal activity near Lake Taupo and other natural sources downstream.

The slight variation noted recently may be due to changes in the river arsenic caused by environmental or other factors. Waikato Regional Council are investigating the variation.

Has all Waikato District’s treated water supply got slightly elevated levels of arsenic?

No – the raised levels of arsenic are only in treated water supply from the Waikato River. Treated drinking water supply in Raglan, Port Waikato and Onewhero is not affected.

What are the levels of arsenic being recorded at Waikato district’s other water treatment plants by the river?

Tests are being carried out daily at Huntly, Ngaaruawaahia and Te Kauwhata water treatment plants. Results are expected from today (28 November).

With a test result of 0.011 recorded at Watercare’s plant that supplies Tuakau, Pookeno and Auckland, and a test results of 0.0113mg/litre and 0.0115mg/litre from Hamilton’s water treatment plant, means that it is assumed that levels are similar at our three treatment plants between those two sites.

What’s the plan if arsenic levels remain at a similar level over the next few days or further?

There are plans in place. First options would be to amend the treatment process and introduce chlorine to the front end of the treatment process rather than just at the end when the water is sent to the reticulated network.

This will help capture the arsenic as it goes through coagulation and filtration and lower the levels of arsenic to Drinking Water Standards level.

Will arsenic in my water cause health problems?

Our advice, supported by Health New Zealand and Taumata Arowai, is that our water supply drawn from the Waikato River remains safe to drink.

Limits set under Drinking Water Standards are very conservative and are based on health impacts at high doses over a lifetime. Health impacts from drinking water with slightly elevated levels for a short period of time are not considered likely to result in similar impacts.

What if I'm pregnant, bottle feeding, on dialysis or have other medical issues?

Our advice, supported by Health New Zealand and Taumata Arowai, is that our water supply drawn from the Waikato River remains safe to drink.

While the risk is extremely low, people who may be especially vulnerable, such as dialysis patients, pregnant people or babies, could use bottled water for drinking or cooking as a precaution. They should contact their GP or Healthline if they have concerns.

Will boiling water remove the arsenic?

No. Unlike bacteria, boiling water does not remove arsenic.

 
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