Elevated arsenic levels found in Waikato River affecting Auckland, Waikato water supplies

Elevated levels of arsenic have been found in the Waikato River, affecting water supplies in Auckland and Waikato.

The Water Services Authority, Taumata Arowai, has confirmed slightly elevated - but safe - levels of arsenic.

The authority says it is not yet known what has caused the issue, but reassures people it is safe to drink from the taps.

The 'maximum acceptable value' for arsenic in New Zealand drinking water is 0.01milligrams per litre, it says.

Watercare reported a result of 0.011 milligrams per litre in a sample taken on 25 November.

Hamilton City Council's testing on 19 and 20 November recorded results of 0.0113 and 0.0115 milligrams per litre.

The results of further sampling is expected on Thursday.

Samples taken earlier this month showed arsenic levels below the limit in drinking water standards.

'Safe to drink'

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

"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."

Waikato Regional Council Environmental Science manager Dr Mike Scarsbrook says the Waikato River was known to have elevated arsenic levels primarily because of geothermal activity.

Monthly freshwater testing is done in the Waikato River and 7 November tests 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."

Watercare said the river supplied about 20 percent of Auckland's drinking water.

Chief operations officer Mark Bourne said since detecting the increased result, it has reduced production at its Waikato Water Treatment Plant and increased production at its major Ardmore plant, which treats water from four dams in the Hūnua Ranges.

"This extends the processing time at the plant, and we expect it to improve our ability to reduce the level of arsenic in the treated drinking water," Bourne said.

"We've also stepped up our sampling at the treatment plant and within the distribution network, which includes sampling our blended water at the Redoubt Road reservoir.

"We're working closely with other agencies and will continue to share information as we learn more."

Local Government Minister Simeon Brown says he was briefed on the matter this evening.

He says the water suppliers have been asked to take appropriate steps and communicate concerns with their customers.

Councils respond

Hamilton City council said arsenic levels have been stable in the city's drinking water for many years at below 0.0100 milligrams per litre.

"Ensuring the quality of our drinking water is a top priority for Council and our waters team," Three Waters unit director Maire Porter said.

"While we are conducting additional testing, we want to reassure the community that we are taking the advice of Taumata Arowai, the drinking water regulator, and working diligently to make sure our decisions are based on the most accurate information available."

Waikato District Council said Watercare operates the local water networks under contract in its district.

"Pōkeno and Tūākau are supplied by Watercare's Waikato Water Treatment Plant. There are also treatment plants that serve the townships of Huntly, Te Kauwhata, Meremere, Taupiri and Ngāruawāhia. Samples from these plants are currently being tested, with results due [Thursday]."