The main sources of fluoride contamination of water are fluorite deposits (e.g. Pennine mining areas) and run-off from industrial processes. Fluoridation of domestic water supplies increases the fluoride content to 1 mg l-1. It is extremely unlikely that fluoride deposition occurs at a sufficiently high rate to increase the fluoride content of water even to that level, let alone to toxic levels. Therefore no critical load is recommended and the following is provided solely as background information.