Activated charcoal DOES NOT remove fluoride from water nor does it remove it from your body. There are only three things I am aware of used for fluoride removal and that is:
1)Activated Alumina - this is not rated for internal use nor do I presume that it would be safe.
2) Red Clay - There have been some studies published out of India where natural Red Clays were used to remove fluoride from water but it required that the water be in contact with the clay media for a minimum of 15 min. For absorption to take place. It is likely that a food grade red clay or even a food grade zeolite clay would be able to remove fluoride internally.
3) Reverse Osmosis - does remove fluoride from water. Additionally, as others here have mentioned, food grade sodium tetraborate (borax) has been shown in clinical trials to induce chelation of fluoride compounds from the body via the urine.