Four water suppliers which draw water from the Waikato River have returned arsenic results that meet New Zealand’s drinking water standards.
The suppliers involved include Waipā District Council, Hamilton City Council, Waikato District Council, and Watercare.
Last week, an elevated level of arsenic was found in two drinking water suppliers which treat water from the Waikato River.
Water Services Authority – Taumata Arowai head of operations Steve Taylor today expressed cautious optimism about the results.
“The results have been heading in the right direction for several days and are now within the acceptable range,” he said in a joint media release with the affected councils and Watercare.
Taylor said there was no threat to human health and the water has remained safe to drink throughout the process.
“All water suppliers are continuing their daily testing for the time being.”
Watercare gathered samples from the river and at each stage of the water treatment process earlier today. The samples will be sent to a specialist laboratory in Melbourne for analysis to confirm the species of arsenic present.
The results, expected within seven to 10 days, will help determine the most effective treatment processes for its removal.
The findings will also be shared with Taumata Arowai, the Waikato Regional Council, and other water service providers.
Hamilton City Council
Hamilton City Council testing has now shown three consecutive tests which again meet the applicable Drinking Water Standards.
The council’s incident management team said the reporting trend is encouraging but monitoring and testing is ongoing.
Hamilton’s water remained safe to drink and for all normal use at all times.
Waipā District Council
Levels of arsenic in drinking water from all three treatment plants in Waipā have returned to below Drinking Water Standards’ maximum acceptable values, the Waipā District Council said today.
“Yesterday evening’s results recorded 0.0078 and 0.0097 milligrams per litre from the two main treatment plants, down from 0.01 and 0.011 on Monday, and the original results of 0.0138 and 0.0145,” water services manager Karl Pavlovich said.
The Alpha St plant results were 0.0078 milligrams per litre yesterday, down from 0.0117 on Monday.
The maximum acceptable standard for arsenic in New Zealand drinking water is 0.01 milligrams per litre.
Pavlovich said while the drop in arsenic levels was welcome news, the council will continue to test the water daily as part of their “enhanced arsenic monitoring plan” over the next few weeks, as well as reviewing its regular monitoring programme.
“We’d like to collect more data on both the source of the arsenic and how the effectiveness of our treatment can be improved,” Pavlovich said.
Waipā draws some of its water from the Waikato River, where naturally occurring arsenic levels are generated by geothermal activity and accumulated arsenic sediments within the hydro lakes along the river.
Waikato District Council
Waikato District Council said operational changes at its Ngāruawāhia treatment plant have ensured arsenic levels in treated water sourced from the Waikato River are remaining 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.
Watercare Waikato adjusted its treatment process by introducing chlorine at the front end to optimise existing arsenic removal procedures after recording a test result of 0.011 mg/litre on Sunday — just above the 0.01mg/litre MAV under Drinking Water Standards.
Test results since the chlorine was introduced measured 0.01mg/litre, 0.0061mg/litre, and a result today of 0.0081mg/litre.
All test results from Waikato District Council’s Huntly and Te Kauwhata treatment plants have been well within the MAV.
Waikato District Council waters manager Keith Martin said the council will continue to monitor their plants on a daily basis.
“Our operations and maintenance contractor, Watercare Waikato, are also exploring other ways we can continue to improve the operation of the Ngāruawāhia plant specifically and our other plants generally.”
The arsenic level in treated water supplied by Watercare to residents in Tuakau and Pōkeno today recorded a result of 0.0064mg/litre — remaining well below the MAV.
Increased routine monitoring considered
Waikato Regional Council is investigating the feasibility of stepping up its monitoring of the Waikato River over the next two years to improve understanding of the drivers of arsenic concentration and speciation.
The council routinely monitors water quality at 12 sites along the river, with field measurements and water samples collected monthly for testing of a wide range of physio-chemical and microbial parameters. The results are reported through its ‘state of the environment’ report.
Testing of samples collected from a number of sites on the Waikato River between Lake Ōhakuri and Rangiriri last week found that total arsenic levels were within the normal long-term range.
While there had been a small increase in the amount of dissolved arsenic in the water, council scientists believe the current situation is likely due to a change to an alternative chemical form of arsenic — from arsenic (V) to arsenic (III) — which can be harder for treatment plants to remove.
Waikato Regional Council environmental science manager Mike Scarsbrook said the council is investigating the feasibility of expanding the suite of testing on the Waikato River over the next two years.
“We believe a long-term study would enable us to gather the robust data needed to build on historical studies on arsenic in the Waikato River, including in hydro-lake sediments which are a known source of different forms of arsenic,” Scarsbrook said.
“It would give us a better picture of what’s happening in the river and perhaps get us to a point where we might be able to predict incidents, like the one we are experiencing, in the future.”
Scarsbrook said a decision would be made on the long-term study in the coming weeks.
Further samples have been collected from the Waikato River over the past three days, as part of monthly monitoring, with the results to be available next week.
While current arsenic levels do not affect contact recreation activities in the Waikato River, people have been encouraged to check the Land Air Water Aotearoa (LAWA) website for the latest advice.
