Retired nutritionist and college lecturer Elizabeth McDonagh, aged 82, of Thorne, is the former chairwoman of the National Pure Water Association.
She has fought councils up and down the country and has lobbied the EU in Brussels on fluoridation.
Doncaster Council voted against endorsing fluoridation in 1997.
But Dr Rupert Suckling, the council's director of public health, raised the issue again after shocking stats revealing the poor oral health in children.
He added adding fluoride returns Â£12 to Â£1 spent in health benefits and residents in areas with the element in drinking water have lower levels of tooth decay.
But Ms McDonagh has claimed countless academics have proven exposure to fluoride has links to skeletal and dental fluorosis and other health conditions.
A similar debate which is further advanced rages nearby in Hull. Councillors are split on the idea and those rejecting fluoridation has prompted a strong response from the British Dental Association to urge opponents not to '˜peddle myths' or '˜alternative facts'.
Responding to the '˜conspiracy theory' labels, Ms McDonagh said: 'If you look at when they piloted it in four areas of the country in the 1940s - the evidence is clear.
'A doctor from the time compared North Shields and South Shields - one had fluoride one didn't.
'He found mortality rate was higher in the fluoridated area. In Birmingham, which has had fluoride in water since 1964, there is evidence now to suggest the neo-natal death rate are higher by around double on average. These are just a few examples.'
Ms McDonagh also claimed Yorkshire Water would be '˜laughing all the way to the bank' if the council paid them to carry out a feasibility study.
'When I read what health bosses were proposing I felt sick to be honest. I can't be as vociferous as I once was as I'm retired but over my dead body will the council carry this out in Doncaster,' she said. Â
'There are better ways to improve children's teeth. Scotland decided a few years ago not to fluoridate and they have something called Child Smile which is a scheme which specifically targets children that need it as opposed to this ridiculous idea in a blanket scheme which goes in all the water.
'There is a big difference between fluoride in toothpaste and adding fluoride to water. There is lots of evidence in children that it is beneficial.
'But the most concerning issue is seems like the council are saying we must give this medicine to everybody regardless of their age, if its good for children in the womb, babies, the elderly, anybody who lives in the area.
'Is it ethical to be giving it to the toothless elderly who might be getting skeletal fluorosis in their old age in order to benefit the teeth of a selection of five-year-olds?
'The reason, is not because of a lack of fluoride in young children, it's because parents give their children drinks and sweets that are extremely high in sugar.'
Dr Rupert Suckling, director of public health at Doncaster Council said: 'The evidence is clear that fluoridation of water can prevent tooth decay, however any decision would need to meet with public approval, be technically feasible and follow Council decision making processes.'