Flouride is a neurotoxic agent. My own opinion is that adding it to the water supply represents complete insanity. In addition the equipment that introduces the flouride may fail and certain batches of water may contain high doses. Years ago I was involved in taking water samples for a project measuring flouride and was surprised at the variations. That being said there may be micro-organisms in the water and a good filtration system is always an excellent idea.
Ever since we installed a water filter, we don't have this problem. Before this we had some stomach trouble. And you can become allergic or lactose intolerant to milk overnight. Maybe it's the fluoride in your water. If you are really concerned about this, bring some water to a boil in a pan. Remove from heat and let sit until cool. Or you could add 2 drops of clorox to a gallon of water.