Cromwell’s water supply is getting a temporary boost: The town will borrow an ultraviolet (UV) treatment unit from Queenstown Lakes District Council to reduce the risk of protozoa contamination while its new water treatment plant is being built.  

The decision at a council meeting on Wednesday (August 27) follows a report from Central Otago District Council’s three waters group manager Julie Muir, which flagged “the Cromwell water treatment plant is non-compliant for protozoa treatment”.  

Protozoa are single-celled organisms – including cryptosporidium and giardia – that can survive in untreated water and cause serious stomach bugs in humans. 

Julie said national water regulator Taumata Arowai had made it clear councils must have “basic barriers in place” and be transparent with consumers “when their drinking water may be unsafe”. 

The new plant was supposed to be ready in December, but commissioning has been pushed back to May 2026. That delay creates a risk period, which council staff say requires a quick fix to avoid the possibility of a boil water notice. 

Julie explained the issue comes down to Cromwell’s water being drawn from bores beside Lake Dunstan that are a mix of aquifer and lake water.  

“The Cromwell supply will source increased volumes of lake water when demand increases in the summer months,” she said in her report.

“The risk from a potential protozoa contamination event cannot be mitigated without an ultraviolet system being in place.” 

Council staff arranged to borrow a containerised UV plant no longer needed in Queenstown for a lease cost of $500 per month – a fee Julie called “a good deal”. 

Total installation and operation costs are estimated at $360,000, to be paid for from the budget already assigned to the wider upgrade project. 

During the meeting, Cromwell councillor and deputy mayor Neil Gillespie emphasised the importance of acting to prevent protozoa contamination. 

Referencing the 2023 cryptosporidium outbreak in Queenstown and a subsequent months-long boil water notice, he said: “It happened just next door in Queenstown. Who would have thought it could happen there? This is the right thing to do and, unfortunately, this doing the right thing comes at a significant cost.” 

Mayor Tamah Alley cited the Havelock North water crisis to highlight the stakes. She spoke of a six-month-old baby who spent nine months in hospital with “ongoing lifelong medical conditions from drinking water that was contaminated”. 

Elected members also suggested the project is an example of growing cooperation between neighbouring councils. 

Council staff will now proceed with decommissioning, transporting, and installing the UV unit in Cromwell.  

The Cromwell Water Safety Plan will be updated to reflect the temporary treatment process and re-submitted to water regulator Taumata Arowai. 

Have a story to share or comment to make? Contact [email protected]