In a statement on Wednesday morning, the council’s infrastructure manager, Joshua Rendell, said fluoridation was to begin again from yesterday.
It was "paused" on October 10 after a problem was flagged to council earlier that month.
Mr Rendell said the issue had been an error in the dosing calculation, and the analyser which reported the fluoridation level in the water.
A subsequent independent test confirmed the original anomaly.
The council started fluoridation last July following a directive from the director-general of health, Dr Diana Sarfati.
Mr Rendell said the levels before October 10 were "within the acceptable values for drinking water". But daily testing of the supply would now be done, "until fluoride is present in the supply".
It would then switch to a weekly regime to ensure fluoride was between 0.7 and 1.0 parts per million (ppm) across the supply. The target level is set at 0.8 ppm.
Mr Rendell said the council believed it was in line with the law.
"The director-general of health completed her Bill of Rights analysis relating to the directives to fluoridate in December 2024. All cases brought before the High Court have confirmed that the directives are lawful."
"All further inquiries" should be directed to the Ministry of Health, Mr Rendell said.
Fluoride Free Waitaki spokeswoman Sheryl Black said the council should listen to its constituents and not comply.
"We are disgusted that the Waitaki District Council has chosen to recommence dosing Oamaru's drinking water with fluoride chemicals.
"They unquestionably should be erring on the side of caution and leaving it turned off," she said.
The compound posing an "unreasonable risk of harm" to human health was backed by "overwhelming recent scientific evidence" and a US Federal Court ruling, Ms Black said.
"We don't believe WDC is meeting its legal obligation under the Health Act to protect public health and to remove any condition likely to be injurious to health."
The council had the option, as stated by Justice Radich in his June 2024 High Court ruling on the case between New Health New Zealand and the director-general of health, to seek an interim injunction.
"An interim injunction would keep fluoridation suspended in Oamaru until the outcome of this court case is heard.
"WDC will say that [Dr Sarfati] has completed her Bill of Rights analysis, but that is only her opinion."
In the meantime, the High Court had yet to decide whether Dr Sarfati’s directives were unlawful — unlikely until late this year.
