You can't see it or smell it, but it's there. And there's a lot of controversy over its health effects on you and your family.

Fluoride has been a regular addition to tap water all over North America for some time, but recently its presence has been causing a little extra stir.

That's mainly because of a 2007 Health Canada panel that recommended the fluoride levels in water be reduced. The drug, which is said to help remineralize the enamel in teeth, thus helping to prevent cavities, has been tentatively linked to a rare type of bone cancer like the type Terry Fox had, not to mention the possibility of reduced intelligence in children and impaired thyroid functionality.

The panel concluded that although there was not enough evidence to draw a link between fluoride and cancer, the maximum amount in drinking water should be reduced to prevent over-consumption, which can cause a condition called fluorosis in children.

Environmental groups held a press conference Thursday, and maintained that their experts' research revealed the long-standing substance used to prevent cavities actually has few benefits, and could pose significant harm.

"Studies are showing that the addition of fluoride to municipal water supplies is having little effect on oral health," explained Karen Buck of Citizens for a Safe Environment.

"The proper toxilogical studies have not been done," said Cindy Mayor of People for Safe Drinking Water. Some activists complain that Canada hasn't taken the time do studies of its own.

Many people argue that the issue should not be decided by the dental lobby, which may be inclined to see health as being all about the teeth, thereby neglecting the rest of the body.

But dental and health professionals are firing back, defending the widespread use of what they consider a helpful substance.

"Health Canada supports water fluoridation as a public health measure to prevent dental decay," said Health Canada's Chief Dental Officer Dr. Peter Cooney. "The big advantage of water fluoridation is that it benefits all residents in a community, regardless of age, socioeconomic status, education, or employment."

"Fluoridated water is the safest and most equitable way of improving oral health for Torontonians of all cultural and socioeconomic backgrounds," agrees Dr. Hazel Stewart of Toronto Public Health.

Click here to find out what the Canadian Cancer Society has to say about its health risks and benefits.

For more info on where in Canada fluoride is added to the drinking water, [see Table below].