Southern councils should expect a letter from water regulator Taumata Arowai reminding them of their responsibilities, even as Queenstown's Cryptosporidium outbreak continues.
A regulator spokeswoman said TA was looking at which councils did not have treatment for protozoa and would write to those councils, outlining "our expectations and regulatory approach".
More than 30 people have been affected by the Cryptosporidium outbreak in the Queenstown Lakes District Council’s (QLDC) water treatment system.
A week after a boil-water notice was put in place for parts of Queenstown, the council and Te Whatu Ora Health New Zealand (HNZ) are no closer to finding the source of the outbreak.
The Otago Daily Times contacted the other southern councils about their water treatment supplies.
Most were confident they had the systems in place needed to prevent an outbreak.
A Waitaki District Council spokesman said 91% of registered Waitaki water supply customers received water that was at low risk of having Cryptosporidium because supplies had both a chlorine bacteria barrier and a protozoa barrier.
"Of the non-upgraded supplies, Omarama would have cartridge and UV in the soon-to-be-completed upgrade, while the remainder had assessments relating to upgrades, or were managed by external parties," he said.
A Dunedin City Council spokesman said it had protozoa barriers in place at all of its water treatment plants.
Central Otago District Council’s spokeswoman said although all supplies needed to be chlorinated to treat bacteria, the requirements to treat protozoa were more complex.
"This typically requires some form of filtration and UV," she said.
"Membrane filters are one type of filter that do not require UV, but these are significantly more expensive to construct and operate."
Of its supplies, Lake Dunstan, Naseby, Roxburgh and Pisa Village were treated for bacteria and protozoa.
Omakau, Ranfurly, Patearoa and Cromwell were treated for bacteria, but not protozoa.
The spokeswoman said the council was investigating options to provide a resilient and compliant water supply.
Gore District Council’s spokeswoman said the council had protozoa treatments in place at its East Gore and Mataura water treatment plants.
East Gore had a membrane system, while Mataura had a sand filter and UV.
A Southland District Council (SDC) spokesman confirmed the council "has not experienced anything like the problems encountered by QLDC" and that SDC used ultraviolet treatment for protozoa.
Invercargill City Council (ICC) three waters technician Adrian Cocker said Invercargill sourced its drinking water from a river catchment that was highly influenced by pastoral and horticultural farming.
"As such, the source water is regarded as having a high risk of containing protozoa before treatment."
He said the ICC water treatment plant had two treatment technologies (or barriers) for removing protozoa.
"The first is a conventional coagulation, sedimentation and rapid sand filtration process which physically removes protozoa from the water.
"The second is an ultraviolet irradiation process that inactivated any protozoa such that they are unable to multiply and thus an infective dose cannot occur," Mr Cocker said
These would probably be the most common protozoal barriers used in drinking water treatment in New Zealand, although others did exist, Mr Cocker said.
On Saturday, Queenstown Lakes District Mayor Glyn Lewers said he expected to have an update on a timeframe for installing an ultraviolet water filter at the Two Mile intake by the end of this week.
The filter was being sent from the Waimakariri District Council.
He had previously said a permanent solution could cost the QLDC as much as $30 million.
