Water supply and arsenic

Slightly elevated arsenic levels in treated water supply from Waikato River at Ngaaruawaahia

Updated 6pm, 28 November 2024.

Only one of Waikato District Council’s water treatment plants recorded slightly elevated arsenic levels in treated water, test results showed today.

A sample of treated water submitted this week from the Te Kauwhata plant showed a reading of 0.0054 mg/litre, well within Drinking Water Standards for arsenic levels of 0.01mg/litre.

A sample of treated water submitted this week from the Huntly plant showed a reading of 0.0089 mg/litre.

Watercare Auckland also received an improved result from its plant near Tuakau, which supplies Pookeno and Tuakau.

The 0.0081 milligrams per litre result in a sample taken yesterday is also within the maximum acceptable value under the Drinking Water Standards.

But a slightly elevated reading of 0.012mg/litre was received from Ngaaruwaahia water treatment plant.

Despite the slightly elevated reading, treated water from the Ngaaruawaahia plant remains safe to drink

Limits set under Drinking Water Standards are very conservative and would require high doses over a lifetime for there to be a health risk.

While the risk is very low, if people still have concerns they should contact their GP or Healthline.

Boiling water before use is unnecessary and not recommended.

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.

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No cause for concern after slightly elevated levels of arsenic detected in water supply

27 November 2024

Watercare has reported slightly elevated levels of arsenic in recent samples of treated water from its plant near Tuakau.

There is no immediate risk to public health.

The ‘maximum acceptable value’ for arsenic in New Zealand drinking water is 0.01milligrams per litre.

Watercare reported a result to national water regulator Taumata Arowai of 0.011 milligrams per litre in a sample taken from its water treatment plant near Tuakau on November 25.

This plant supplies water to Tuakau and Pookeno.

Hamilton City Council also found slightly elevated levels in their testing on 19 and 20 November ands recorded results of 0.0113 and 0.0115 milligrams per litre, which were also reported to Taumata Arowai.

Further sampling has been carried out and Taumata Arowai will receive the results of these tomorrow.

Tests are being carried out at Waikato District Council's Huntly, Ngaaruawaahia and Te Kauwhata water treatment plants.

Previous samples taken earlier in the month by Watercare showed levels of arsenic below the limit in the drinking water standards.

National Public Health Service regional clinical director Dr William Rainger says: “People who are drinking water sourced from the Waikato River do not need to be alarmed.

"The limits in the New Zealand Drinking Water Standards are based on the level of risk from a lifetime of drinking the water.

“Drinking water with slightly elevated levels for a short period of time is unlikely to impact people’s health.

“You do not need to boil your drinking water. It is safe to drink.”

Meanwhile, arsenic is known to be elevated in the Waikato River, primarily due to geothermal activity, says Waikato Regional Council Environmental Science manager, Dr Mike Scarsbrook.

“We undertake monthly freshwater testing on the Waikato River. Testing was last carried out on 7 November and the arsenic levels were not unusual. These levels are typically above the drinking water standard, which is why treatment is required before drinking water is supplied to households.”

As a result of water suppliers alerting the regional council to elevated arsenic levels after treatment, environmental monitoring staff have collected samples from a number of locations along the Waikato River including at Narrows Landing, Horotiu and Rangiriri.

“The laboratory is prioritising testing and results are expected during the day on Thursday, which will be analysed by scientists from the council and Taumata Arowai.”

In the Waikato District Council area, Watercare operates the local water networks under contract. Pookeno and Tuakau are supplied by Watercare Auckland’s Plant near Tuakau.

There are also treatment plants at Huntly, Te Kauwhata, and Ngaaruawaahia.

Samples from these plants are currently being tested, with results due tomorrow, and testing will be done daily.

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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.