There is no clear evidence that fluoridated drinking water increases cancer risk, however there is very good evidence of its benefits in reducing tooth decay, which is a major public health problem. As a result, most health authorities around the world recommend fluoride continue to be added to drinking water to prevent and repair tooth decay. Fluorides occur naturally in water, soil and air; nearly all water contains some level of fluoride. In many countries, and most regions of Australia, fluoride is added to drinking water because of its proven public health benefits in reducing tooth decay. Hundreds of studies about the safety and effectiveness of water fluoridation have been conducted. In 2007, Australia’s National Health and Medical Research Council identified more than 5000 research papers and reviewed 77 good quality studies. It recommended that water fluoridation continue, as the evidence showed it reduced tooth decay and that there was no clear association with cancer. A World Health Organisation review also concluded that there was no clear or consistent link between fluoridated water and any type of cancer. Because fluorides that enter the body tend to collect in areas high in calcium such as bones and teeth, several studies have looked at the possibility of a link between fluoridated water and osteosarcoma – a rare, but serious bone cancer. A US study in 1990 found male rats given high doses of fluoridated drinking water had higher rates of osteosarcoma. But more recent studies, including studies measuring bone fluoride concentrations in people with osteosarcoma and people without any bone cancer, have not shown the same link.