Upgrades to the Patearoa and Ranfurly water treatment plants are under way and should be finished by the end of the year.
Central Otago District Council capital projects programme manager Patrick Keenan said the upgrades would include the installation of protozoa barriers, to meet New Zealand drinking water quality assurance requirements and provide more reliable, safe drinking water.
Both towns’ water sources were prone to high turbidity — cloudiness caused by suspended particles of silt, clay and organic matter — particularly after heavy rainfall, which could compromise water treatment effectiveness and lead to boil water notices.
Yesterday, the council advised Ranfurly was on a conserve water notice from 6pm due to recent rain.
The improvements were planned infrastructure upgrades with the $4.2 million budget allocated in the council’s 2024 annual plan and 2025 long-term plan.
Mr Keenan said the council had considered options for the upgrade — including building new treatment plants at about $15m for Patearoa and $21m for Ranfurly — and landed on cartridge filters and ultra-violet protozoa barriers.
Ultraviolet light would neutralise harmful micro-organisms, including protozoa, replacing existing treatment processes.
Once the upgrade was completed, the communities should see fewer boil water notices, Mr Keenan said.
However, it would not solve all water quality issues, particularly during severe weather events, he said.
The contract for the work was awarded to Fulton Hogan in May.
"Council has worked closely with Fulton Hogan’s design team to develop a cost-effective and practical upgrade plan, with the concept design now approved and coming in well under the initial $4.2m budget," Mr Keenan said.
It was estimated the Ranfurly upgrade would cost about $1.7m and Patearoa about $1.6m.
Both water treatment plants source water from surface water — the East Eweburn River for Ranfurly and Sowerburn River for Patearoa — and are vulnerable to turbidity following heavy rain.
The Ranfurly treatment plant consists of sand filtration and chlorination, and Patearoa has chlorination only. Those systems treat for bacteria but not protozoa.
Protozoa such as Cryptosporidium and Giardia can be spread through water supplies without protozoa barriers or treatment.
In September 2023, an outbreak of cryptosporidiosis in Queenstown was linked to inadequate water treatment filtration. That year, water services authority Taumata Arowai identified 27 councils around the country, including Central Otago District Council, that did not meet the standards for protection from protozoa.
