Whoa, you would test people on whether they are truly libertarian or not?  Need me to recite the non-aggression oath?  

Back to fluoridation:  People who have the unreasonable fear that their body absorbs fluoride ions through the skin will need to filter their water regardless of whether it has optimal fluoridation levels or the suboptimal levels found in the local ground water.  

Yes, almost all ground water has fluoride, which is why humans evolved a need for this mineral nutrient which is responsible for helping us have strong bones and teeth.