Water supply and arsenic

Arsenic level in treated water supply meeting Drinking Water Standards

Updated 4.20pm, 4 December 2024.

Operational changes at Waikato District Council’s Ngaaruawaahia treatment plant have ensured arsenic levels in treated water sourced from the Waikato River are now within the maximum acceptable value (MAV).

This plant is the only one in the district that has recorded slightly elevated levels of arsenic in the drinking water supply during the past week.

After a test result of 0.011 mg/litre was recorded on Sunday, just above the 0.010 mg/litre MAV under Drinking Water Standards, Watercare Waikato has adjusted the treatment process by introducing chlorine at the front end to optimise existing arsenic removal procedures.

This is working, as test results since the change have measured 0.010 mg/litre, 0.0061 mg/litre and today’s result of 0.0081mg/litre.

All test results from the Huntly and Te Kauwhata treatment plants have been well within the MAV, with today’s being 0.0054 mg/litre and 0.0024 mg/litre respectively.

The arsenic level in treated water supplied by Watercare to residents in Tuakau and Pookeno also remains well below the MAV, with today’s result being 0.0064mg/litre.

And the latest results from Hamilton City Council, who supply treated drinking water to the Tamahere-Woodlands Ward, have showed a continued reduction in arsenic levels with the city’s drinking water supply meeting the applicable Drinking Water Standards for three consecutive days.

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 supplied to Waikato district residents has remained safe to drink and for all normal use at all times.

Read the latest news

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

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.