Principal dental officer for community oral health Dr Rob Aitken said a study of 16,500 children in Australia showed there was a big reduction in tooth decay for those who drank sugar-sweetened drinks but had access to fluoridated water.
"Given we consume more sugar per capita than Australia, the US or Great Britain then if you take fluoride out of the water and fluoride reduces decay - the logical outcome is decay is going to increase," he said.
"We can't access everyone to teach them how to brush their teeth and that's the biggest problem ... it's the children in the lower socio-economic groups that don't even have toothbrushes, it's those kids who are hardest hit."
Mayor Julie Hardaker, who tabled the motion to remove fluoride, said the issue was a public health matter that central government needed to determine.
But deputy mayor Gordon Chesterman said there was "a lack of clear proof" of benefits in fluoridation as well as a continuing reduction in support for it with just 23 of New Zealand's 67 local authorities using it in their water supplies.
A $160,000 referendum of Hamilton City voters in 2006 drew 38 per cent of voters - 70 per cent of whom voted to keep fluoridation. But during a campaign for public input the tribunal received 1560 submissions - with 89 per cent (1386) opposed to fluoridation.