Although current studies of the effectiveness of water fluoridation have design weaknesses and methodological flaws, the balance of evidence suggests that rates of dental decay are lower in fluoridated than non-fluoridated communities. The magnitude of the effect is not large in absolute terms, is often not statistically significant and may not be of clinical significance. The effect tends to be more pronounced in the deciduous dentition. The effect tends to be maximized among children from the lower socioeconomic groups so that this section of the population may be the prime beneficiary. Canadian studies do not provide systematic evidence that water fluoridation is effective in reducing decay in contemporary child populations. The few studies of communities where fluoridation has been withdrawn do not suggest significant increases in dental caries as a result. More research is needed to document the benefits of fluoridation to adult and elderly populations in terms of reductions in coronal and root decay. Research is also needed to document improvements in the oral health-related quality of life that accrue to populations exposed to fluoridated water in order to enhance the credibility of this public health initiative.