Fluoride is good. Fluorine (the elemental form of it) is bad. Most everyone who thinks they have something to say about fluoride gets the hazard info for fluorine. Just as elemental sodium is quite toxic (it will explode on contact with water) it's essential when mixed with chlorine (another very toxic element) in the body. Nothing would work without it. Fluoride is a critical part of bone synthesis and is quite good at preventing dental caries.

Fluoridating water (where needed) has improved dental health tremendously in the US, and dental health has significant health implications for the rest of the body. When I go to the dentist (twice a year) I get a fluoride rinse.

For chemical water purification I like polar pure - elemental iodine crystals. Follow the directions. It doesn't go bad, which is an improvement over any of the pills. However, killing pathogenic organisms doesn't take care of chemical pollution, so I prefer filters when possible. I use the MSR/Sweetwaters, it seems like it has a good price/performance point. Ceramic filters like in the Katadyne (also a good brand, but pricey) have problems with freezing and cracking, while the instructions for the MSR say to store wet filters in the freezer between trips (I just replace them).