Water supply and arsenic

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.

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.

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.

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.

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.

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.

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.

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