HB DHB clinical director for oral health Robin Whyman said that yearly reports had been completed since the council's decision and the results showed that Year 8 children were now 55 per cent cavity-free compared to 65 per cent before the fluoride was removed.
More striking, in the younger age group and when ethnicity was considered as well, the number of 5-year-old Maori children who were cavity-free had dropped from 54 per cent to 24 per cent.
"It's showing what international evidence tends to tell us that community water supply fluoridation plays a big part in preventing dental decay.
"CHB is an example of what happens when you take it away and how it opens up the deprivation gap quite quickly."
Across Hawke's Bay, Wairoa and Napier have fluoride-free water supplies, but Hastings water had been fluoridated since the 1950s and a 2013 referendum confirmed the community supported its retention.
As a result of last year's Havelock North campylobacter outbreak, however, fluoridation had been removed because the injection points into the water supply were being used for chlorination.
Mr Whyman said that although there had been no fully controlled local studies, information from a 2009 New Zealand oral health study showed there was generally 40 per cent more presence of dental decay in communities that were non-fluoridated compared to those with fluoridation, and a similar statistic was seen when comparing levels of decay between Hastings and Napier.
In addition, among Year 8s who had decay, Napier cases were more serious.
Mr Whyman said the fluoride in toothpaste was not enough, with the New Zealand oral health survey showing people did not brush their teeth as often as they thought they should.
In terms of cost-effectiveness, he said a recent national research report had shown that the net benefit of fluoridated water for communities of 500 people or more over a 20-year period was in the region of $1.4 billion savings for the country.
"Over 20 years Hawke's Bay savings would be between $9 million and $27 million - some of that to the DHB which funds most of the care for children and adults, but the community would also save in terms of dental expenses."
Fluoride Free NZ, however, does not agree with the DHB's stance. Spokesman Don Church said the statistics used to support fluoridation were not robust enough, and could be "cherry picked" to support the Ministry of Health's stance.
He said testing 5-year-old children did not give an accurate picture because they still had their softer, baby teeth, and that figures could be found to show that areas that had stopped fluoridation had seen a decrease in dental decay.
He said that there were dentists and doctors both nationally and internationally who supported Fluoride Free NZ's stance.
"It's not black and white - you can find statistics to support any bias, and with the Ministry of Health so committed to fluoridation it would be difficult for DHBs to go against that."
Last month, Napier resident Matthew Kingi created a petition in response to the bill to protest Napier's water being fluoridated, a position he said a lot of people supported. By the end of the first week of May he had gathered about 310 signatures.
If the legislation was passed, DHBs would be expected to start making decisions about community water fluoridation in 2018.
