How to test for fluoride levels in drinking water?
A good reliable set-up is pricey.  Here's a link to a reliable, quality probe for fluoride ion detection in water, it costs \$740  (US).  The meter that it plugs into sells for \$790 (US) if you get the less expensive hand-held device.  There also manuals and instructions on how to actually use the gear, at the website as well.