A fierce debate is under way in Hampshire over whether to put fluoride in tap water for about 200,000 residents in and around Southampton.
But for years it has been added to drinking supplies for cities such as Birmingham and Newcastle. So why is there still such concern?
Tooth decay is a big problem among children in Southampton.
Last year more than 520 had to undergo general anaesthetics to have a total of 2,900 teeth removed.
So the city's primary care trust wants fluoride added to water supplies to improve dental health.
But the plan, currently at consultation stage, has sparked strong opposition from campaigners who claim it could cause tooth discolouration and other health problems.
Earlier this year residents of the Isle of Man rejected a similar scheme.
But millions of people in England already drink fluoridated water.
In the 1950s pilot schemes were carried out in the UK after some US cities began adding the substance to their supplies.
Today, most of the West Midlands, large parts of the North East and parts of the East Midlands, East and North West have fluoridated water.
In February this year Health Secretary Alan Johnson called for fluoride to be added to more water supplies to reduce tooth decay among some of society's poorest and most vulnerable people.
Prof Michael Lennon, chairman of the British Fluoridation Society, believes there are major health benefits for deprived areas and people are wrong to oppose the move.
He said fears over fluorosis [teeth discolouration] and other side affects were misguided.
"About 10% of the UK is currently fluoridated and our view is we should extend that to about 30% of the population," he said.
"Fluoridation is not a new idea that's been dreamt up, it's as old as the hills.
"We have conducted public opinion surveys for the last 15 years and public support for fluoridation is quite high, 65 to 75% think it's a good idea.
"But 10 to 20% oppose it vehemently. I'm not sure why but I think it boils down to a view about ethics and public health responsibility.
"[Opponents] will use all sorts of statistics about fluorosis. If this is true how come two million people in Birmingham have been drinking fluoridated water since 1964? These arguments just don't stack up."
The British Dental Association (BDA) also backs fluoridation.
"One of the most compelling arguments is it can help reduce health inequalities," a spokeswoman said.
"Six of the top 10 places for children with the best dental health have fluoridated water.
"I'm sure there's an element of fear of the unknown, people don't like things to be added to the water supply.
"I think that's understandable, but equally it's very important that people supporting fluoridation explain the case.
"[Fluoride] is not a poison, it's an occurring mineral.
"The BDA feels very strongly that targeted fluoridation is appropriate to redress serious dental decay."
Less than 1% of people who have fluoridated water suffer from fluorosis, she added.
But Ann Richards, a member of Hampshire Against Fluoridation, strongly disagrees.
The group is drawing up petitions, leaflets and DVDs to distribute to people in and around Southampton arguing against the change.
Mrs Richards said, as well as fluorosis in children, evidence showed fluoride in water could lead to irritable bowel syndrome, rashes and nausea among some people.
"There are a lot of very angry people out there.
"The authorities that put it in the water have no control over the dose that people get," she said.
"There has been no examination of the population to determine what it is doing. It is a vicious nasty poison and it's one that accumulates in the body."
And it is not only people in Hampshire who are opposed to the move.
Several years ago a number of MPs formed the All Party Parliamentary Group Against Fluoridation.
Its chairman Brian Donohoe, Labour MP for Central Ayrshire, said he wanted the public to get the full facts about fluoridation and not be "duped" into accepting it.
"I don't think anything should be added to the water as a medicine, because it's the beginning of the end.
"What's to stop you adding other things as medicine?
"I don't think it should be imposed upon people without them having a say. There has to be a poll of the public."