I think you will find that Auckland water has chlorine and not flouride. Chlorine is added as the gas or HTH which produces 80% of its weight in chlorine gas. Chlorine is used as a disinfectant and chlorination is required to get an AAA rating. Flouride is added as sodium flouride and is added to prevent tooth decay as flouride is low in NZ waters and it is required to build tooth enamel. Flouride is added to some water supplies but I don't think it is added to Auckland water.