Local councils have been directed to add fluoride to some or all of their water supplies.

Director-General of Health Dr Ashley Bloomfield today said he had written to 14 authorities instructing them to fluoridate their water under the Health Act.

Included in the directive are Rotorua Lakes Council, Tauranga City Council, Western Bay of Plenty Council and Kawerau District Council.

It is the first time this power has been used since the relevant legislation was amended last year to ensure a national approach to fluoridating water.

In a statement today, the Ministry of Health said local authorities who are directed to fluoridate their water supplies will be invited to apply for funding from an $11.3 million fund for capital projects associated with these works.

The Health (Fluoridation of Drinking Water) Amendment Act 2021 shifted the decision-making authority on community water fluoridation from local authorities to the director-general of health on the basis that it is a health-based decision.

Bloomfield said fluoridation was proven to be a "safe, affordable and effective method of preventing tooth decay".

"Community water fluoridation benefits everyone, but especially children, Māori, Pasifika and our most vulnerable.

"Water fluoridation helps prevent tooth decay, along with brushing your teeth twice a day with fluoride toothpaste, eating healthy food and avoiding sugary drinks. Fluoride in water acts like a constant repair kit for your teeth," Bloomfield said.

"Fluoridated water is safe for everyone to drink – including babies and the elderly – and fluoride exists naturally in air, soil, freshwater, seawater, plants and in food."

"We estimate that adding fluoride to the water supply in these 14 local authority areas will increase the number of New Zealanders receiving fluoridated water from 51 per cent to around 60 per cent."

Bloomfield said it's likely that later this year he will actively consider whether to issue further directions to fluoridate.

The time each local authority has to fluoridate their water supply varies between six months and over three years, depending on the circumstances of the supply.

The 14 local authorities that have received directives are Whangārei District Council, Western Bay of Plenty District Council, Waitaki District Council, Waipa District Council, Tauranga City Council, Taurua District Council, Rotorua Lakes Council, New Plymouth District Council, Nelson City Council, Kawerau District Council, Horowhenua District Council, Hastings District Council, Far North District and Auckland Council.