Why is fluoride added to water supplies?

To harden the enamel coating on teeth to protect them against decay.

Trace amounts of fluoride can combine chemically with the surface of teeth to make them slightly tougher.

Is it safe?

There have been many concerns over the years but the main worries have focused on cancer, bone diseases such as osteoporosis and developmental abnormalities including Down's syndrome.

Opponents of fluoridation claim fluoride is a toxin that can accumulate in the body.

The new report looked at the evidence behind these claims and found that overall there is no clear reason to be concerned.

For example, as many studies have found decreases in cancer rates in fluoridated areas as have found increases.

And some water supplies have naturally high levels of fluoride.

According to the report, studies of people living in such areas have failed to find clear evidence of harm to people.

Why do some people still object to fluoridation?

Because they think scientists haven't yet looked hard enough for evidence of harm in people; and because studies of the effects of fluoride on animals such as rats have revealed some problems, especially at high doses.

How many water supplies are fluoridated?

In Britain, surprisingly few. About 10% of Britain is supplied with fluoridated water.

Why are some not?

Some local authorities have decided against it because of the health concerns, or because the fear a backlash triggered by anti-fluoride campaigners.

Others have asked water companies to add fluoride only to have the companies refuse.

At present they are private companies that need to make a profit.

They see nothing but potential trouble - and higher costs - in extending the practice of fluoridation.

Some water supplies cannot be easily fluoridated for technical reasons.

Who controls whether fluoridation takes place?

The local authority can invite or request water companies to add fluoride. But they cannot make them.

The government may change that rule in the light of the new report.

What is the government's position?

The Department of Health has dental targets to reach.

More fluoridation would help, so it is pro-fluoride.

On the other hand, the government knows the anti-fluoride lobby is quite adept at mobilising the media on the risks of fluoride.

It wants to avoid being too obviously gung-ho about fluoride and is very keen on making sure local authorities consult widely before making decisions.