Arsenic levels in Waikato River within the ‘usual range’

Joint media release

The results of Waikato River water testing at multiple sites between Lake Ōhakuri and Rangiriri show that arsenic levels are within the normal range expected.

The samples taken directly from the Waikato River have returned results of between 0.0189 milligrams per litre and 0.0256 milligrams per litre. The same sites, based on long term data, are usually between 0.0123 milligrams per litre and 0.03 milligrams per litre.

Environmental monitoring staff from Waikato Regional Council collected the samples on Wednesday after being alerted to slightly elevated arsenic levels after treatment by water suppliers Watercare and Hamilton City Council. Two other district councils – Waikato and Waipā – subsequently also reported slightly elevated levels of arsenic in their treated water.

The Maximum Acceptable Value (MAV) for arsenic in treated water is 0.01mg/L.

In all cases, drinking water remains safe to drink, with arsenic levels now also meeting Drinking Water Standards for Watercare and Waikato District Council.

Waikato Regional Council Environmental Science Manager Mike Scarsbrook describes the arsenic levels detected in the samples of water taken directly from the Waikato River as being within the ‘normal long term range’.

“The results that have come in overnight and during today have been carefully examined by our scientists against historical data.

“While the levels are within the range of normal for the Waikato River, there has been a small increase in the amount of dissolved arsenic in the water. This can be harder for treatment plants to remove, but the change is so small we don’t believe it’s the main cause of the current situation.

“We think it’s more likely to be a change to an alternative chemical form of arsenic, which is known to be more difficult to remove by treatment plants. This change is possibly caused by changes in temperature, dissolved oxygen and pH within the hydro lakes. We’ve seen a similar situation in 2012 and 2013, which resolved itself.

“Our chemists are working with scientists from Water Services Authority – Taumata Arowai and Watercare, and we’re in contact with laboratories in Australia with expertise in the kind of testing required to confirm this cause.”

Arsenic is known to be in the Waikato River in elevated levels, with three main sources:

• Geothermal sources of arsenic from Lake Taupō. Arsenic at the exit point of Lake Taupō is already sitting right on the drinking water standard, but doesn’t vary much at all.

• Geothermal sources of arsenic in the upper Waikato River around Wairakei and Ohaaki. Some of this is naturally discharged and some is a result of geothermal power company discharges – this also doesn’t tend to vary much, although the geothermal power station source has reduced compared to historic discharges.

• Accumulated arsenic in sediments within the hydro lakes along the Waikato River. Lake Ōhakuri is the main source which can undergo seasonal release of arsenic from lakebed sediments in a form that is less easily removed by water treatment plants. This typically happens in summer months when temperatures are warmer.

Current arsenic levels do not affect contact recreation activities in the Waikato River. However, people should always check the Land Air Water Aotearoa (LAWA) website for the latest Can I swim here? advice.

Head of Operations for the Water Services Authority - Taumata Arowai, Steve Taylor, says the Authority is continuing to monitor the situation and work closely with the drinking water suppliers to ensure they are taking appropriate steps to manage and resolve the issue.

“The drinking water suppliers are working to find out what has happened so they can to optimise their treatment processes to reduce arsenic levels to below the MAV.

“We are also working closely with the Waikato Regional Council to understand fully how the changes in arsenic composition are affecting water treatment processes.”

National Public Health Service regional clinical director Dr William Rainger continues to remind people who drink treated water sourced from the Waikato River that there’s no 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.”

New Zealand Food Safety’s deputy director general Vincent Arbuckle says, “The levels detected are not harmful to animals and there is no evidence water used for animals or food production is unsafe. If there was a risk to food safety we would take appropriate action to protect consumers, including recalls.”

Auckland’s water supply continues to meet drinking water standards

Watercare chief operations officer Mark Bourne says the test results from treated water samples taken at Waikato Water Treatment plant have met drinking water standards for New Zealand for three days running.

Watercare results

Date: 28/11/2024

Level of arsenic: 0.0068 mg/l

The ‘maximum acceptable value’ for arsenic is 0.01 milligrams per litre: Compliant

Date: 27/11/2024

Level of arsenic: 0.0062 mg/l

The ‘maximum acceptable value’ for arsenic is 0.01 milligrams per litre: Compliant

Date: 26/11/2024

Level of arsenic: 0.0081 mg/l

The ‘maximum acceptable value’ for arsenic is 0.01 milligrams per litre: Compliant

Date: 25/11/2024

Level of arsenic: 0.011mg/l

The ‘maximum acceptable value’ for arsenic is 0.01 milligrams per litre: Above limit by 0.001mg/l

“We continue to be cautiously optimistic and are continuing our daily sampling programme for the time being.

“Water produced at our Waikato Water Treatment Plant passes through a robust multi-barrier treatment process that includes coagulation, clarification, filtration and absorption processes.

“This treatment process is effective in eliminating a wide range of contaminants, including microorganisms, ensuring safe drinking water.”

Bourne says the company’s operational response includes reducing production at its Waikato treatment plant and increasing production at its Ardmore plant.

“As a prudent water supplier, we’ve made the decision to reduce production at our Waikato Water Treatment Plant while we work with Waikato Regional Council to understand what has caused the changes in river water quality.

“This means we are drawing more water from our dams in the Hūnua Ranges. While we are not in a drought, summer is just around the corner – so we encourage Aucklanders to take it easy with their water use because water is a precious resource.”

Waipā District Council

Waipā water is still safe to use, with today’s test results showing a continued small reduction in the levels of arsenic in the district’s treated drinking water.

The results received this afternoon recorded 0.0128 and 0.0131 milligrams per litre from the two main treatment plants, down from 0.0129 and 0.0143 yesterday, and the original results of 0.0138 and 0.0145.

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

Water services manager Karl Pavlovich said the council has now added the Alpha Street water treatment plant to the testing regime, to ensure it is up to standard when it comes into use over the summer period. The Alpha Street plant results were 0.0125 milligrams per litre this afternoon, down from 0.0126 yesterday.

“We will continue to test daily,” Pavlovich said. “The water remains safe for drinking, bathing, and cleaning, and there is no need for people to boil it.”

The Water Services Authority - Taumata Arowai and Health New Zealand have confirmed that drinking water with slightly elevated arsenic levels for a short period of time is unlikely to impact health, while New Zealand Food Safety says the levels detected are not harmful to animals or to food production.

Waipā draws its water from the Waikato River, which has naturally-occurring arsenic levels generated by geothermal activity.

Testing is done by Hill Laboratories, Hamilton. You can keep up to date with the latest test results and information by clicking here.

Waikato District Council

Levels of arsenic in drinking water from treatment plants in the Waikato District have returned to being under Drinking Water Standards maximum acceptable values.

Today’s test results show treated water sourced from Waikato River being supplied from Ngaaruawaahia, Huntly and Te Kauwhata plants is below 0.01mg/litre.

Results from Watercare Auckland’s treatment plant that supplies Pookeno and Tuakau are also below 0.01mg/litre.

Watercare Waikato will continue to test daily to ensure any fluctuation of arsenic levels are captured.

Hamilton City Council continue to adjust processes

Hamilton City Council’s latest test results this afternoon confirm arsenic levels remain slightly elevated and work continues to bring them down.

“The levels are not yet within the relevant Drinking Water Standard, but our water supply remains safe for everyday use,” Unit Director Three Waters Maire Porter said.

“Making changes to a complex process is not something you want to rush, but we’re making incremental changes with the aim of bringing the levels back down in coming days.”

A combination of approaches are under way or being planned across the weekend and early next week.

Staff at the city’s water treatment plant are optimising existing arsenic removal processes, and a new membrane filtration system, which treats the water in a different way, will be brought online.

In conjunction with industry experts, Council’s specialists are looking at chemical changes to the arsenic during treatment to enable existing systems to remove it more easily.

“We anticipate seeing positive results as we make these changes and will continue to work with the water regulator, neighbouring councils and industry experts.”