An algal bloom in a reservoir that feeds into Dunedin's water supply has resulted in "foul, mouldy-tasting water", and technology to get rid of it could cost up to $25,000.
The Dunedin City Council has been monitoring the problem since late March, but both the council and Public Health South yesterday said there were no health concerns.
The algal bloom was found in a reservoir that feeds the southern water treatment plant, near Brockville.
A Shiel Hill resident alerted the Otago Daily Times to the problem, and said she and her flatmates had found the taste of tap water "awful" for two to three weeks.
"We expect to be able to turn on the tap and drink the water."
Asked if there was an issue in the area, council water operations team leader Gerard McCombie said the council had fielded 30 calls from residents concerned about water quality from April 15 to April 20.
Scientists had been testing the water, trying to identify the species and doing "cell counts", checking whether cyanobacteria was above alert levels, and if it was, doing additional testing for cyanotoxins.
The results did breach alert levels on March 31, which prompted a call to Public Health South water assessors.
Otago-Southland medical officer of health Marion Poore said blue-green algae was also referred to as cyanobacteria, and that could produce cyanotoxins, which could cause health problems.
Testing, which was ongoing, had shown levels of toxins well below those that would raise concern, and there was no risk to health.
Mr McCombie said the council was considering ways to deal with the problem.
The Southern Water Treatment Plant supplied water to a wide area of Dunedin, from Green Island to the Otago Peninsula.
