A study of tooth decay in 11,000 West Australian children has reinforced the dental benefits of drinking fluoridated water.

The research found children in areas without a fluoridated water supply in the South West were 1.5 times more likely to have decayed or missing teeth, compared to children in Perth where the water is fluoridated.

The Health Minister John Day, who is a former dentist, said more than 92 per cent of WA's drinking water had been fluoridated since the policy began 50 years ago.

"It is far better than people having to spend lots of money on expensive dental treatment when it can otherwise be prevented," Mr Day said.

"It's now been known for at least 60 years that having fluoride in water supplies at the appropriate level has a very beneficial effect in reducing tooth decay in the community.

More than 92 per cent of WA's drinking water is fluoridated. ( ABC News )

"But it is good to have up to date information about the situation in Western Australia so that people can be reassured that it is still worth doing."

A petition with more than 8,000 signatures is being presented to the WA Parliament on Wednesday, calling on the Government to abandon its fluoride policy.

The group named Fluoride Free WA is behind the petition and believes ingesting fluoride is dangerous.

But Mr Day dismissed the concerns.

"There is no reputable, scientific evidence from any credible organisation that fluoride in the water at the appropriate level has any harmful effects," he said.

"To the contrary, it has a very beneficial effect."