Adjusting the level of fluoride ions in community water is not consider "drug" delivery. (Nor is the addition of various water treatment chemicals. See Wikipedia on water treatment.)  

The optimal level of fluoride is a level found in nature, and many communities in the USA don't have to fluoridate simply because Mother Nature has blessed them with "just right" amount of fluoride in their ground water.  

As for the issue of "consent," informed consent is necessary for individual medical care.  Consent is not required for public health measures, because they must be demonstrated to be overwhelmingly safe and necessary for the safety and health of the community. For example, other public health measures include the requirement for infant car seats, restaurant hygiene, pasteurization, etc.