§ Mr. SymsTo ask the Secretary of State for Environment, Food and Rural Affairs what investigation she has made of the cost of corrosion damage to water providers in(a) fluoridated and (b) unfluoridated areas. [42973]
§ Mr. MeacherThe maximum permitted concentration of all fluoride in public water supplies is 1.5 mg per litre of water. The effects of public water supplies on water companies' pipes are normally measured by the water's pH although there are other factors. In general, the lower the pH value, the higher the level of corrosion. Legislation specifies two compounds of fluorine which water companies may add to public supplies at the request of area health authorities. The compound that companies would normally add is hexafluorosilic acid. This is a corrosive substance and care must be exercised when it is delivered, in bulk, to water treatment works. There is, however, no measurable change in the pH of fluoridated or unfluoridated water, on leaving the treatment works, and therefore no reason to suspect that fluoridated water is more or less corrosive in the distribution system.