The primary purpose of Ontario Drinking Water Objectives is to protect public health. Most Ontario Drinking Water Objectives are adopted from the Guidelines for Canadian Drinking Water Quality.The Guidelines for Canadian Drinking Water Quality are established via a formal Federal-Provincial process with the participation of Health Canada, Environment Canada, and each of the Provinces and Territories. These Guidelines are established/revised as necessary by the Federal-Provincial Subcommittee on Drinking Water.The Federal-Provincial Subcommittee on Drinking Water (DWS) recently completed an extensive reassessment of the Canadian Drinking Water Guideline for fluoride. Following the completion of this review, it was determined that the current CDWG of 1.5 mg/L is appropriate and should be reaffirmed. However, it was also concluded that the recommended level of fluoride in treated drinking water, where fluoridation of water is practised, should be reduced from the current recommended level of 1.0-1.2 mg/L to 0.8-1.0 mg/L.Fluoride may be added to water during water treatment in order to reduce the incidence and severity of dental caries in the population. Whereas appropriate levels (e.g., 0.8-1.0 mg/L) of fluoride in treated drinking water are considered to be beneficial due to the reduced incidence of dental caries in the population, excessive levels of fluoride in drinking water (e.g.,>1.5 mg/L) may lead to dental and/or skeletal fluorosis unless steps are taken to reduce overall fluoride exposure.Fluoride may occur naturally in surface and ground water and may be found in commercial products such as toothpaste and soft drinks.