The water in Hastings remains fluoride-free, and it is causing major concern among oral hygiene staff at Hawke's Bay District Health Board.
Fluoride was supposed to be added back to the water last year but Hastings District Council group manager asset management Craig Thew said "the dosing system at the treatment plants was being used for chlorine rather than fluoride".
He said fluoride will be added when all the treatment plant upgrades are in place and operational mid-2021.
He added that no measures were being taken in the interim to re-introduce fluoride.
Hastings was the first place in New Zealand to have fluoride added to its urban water as a means of preventing tooth decay, in 1954, but the water supply has been fluoride-free since the Havelock North gastro-outbreak in 2016.
The campylobacter contamination in August 2016 made 5500 people ill and was linked to the deaths of three people. It led to a government inquiry.
Hawke's Bay District Health Board chief medical and dental officer Robin Whyman told Hawke's Bay Today he was concerned there had been a lack of fluoride in the Hastings drinking water supply since 2016.
"By 2021, when Hastings District Council will have fluoride back in all its town water supplies it will mean some 5-year-old children have not ever had fluoride added to their drinking water.
"Adding fluoride to the drinking water supply was highly cost effective and remained the most equitable way to improve the oral health of communities.
"We are working closely with Hastings District Council and are hopeful at least parts of the drinking water supply will have fluoride added before 2021, with the entire network operating with fluoride by 2021."
In the meantime people should make sure they use brush their teeth at least twice a day with fluoride toothpaste, make sure children are enrolled with community oral health services, limit sugary drinks and food, and adults should have regular dental check-ups, he said.