The always-readable Tyler Cowen leaps to a conclusion that seems dubious but may have a grain of truth:

"when you buy bottled water isn't fluoride what you're trying to avoid?"

Well, no. When I buy bottled water, I'm trying to deal with other issues:

convenience (sports caps, since my three-year-old cannot necessarily be trusted with cups)

safety (lead pipes in the house which are not cost-effective to replace, at least not for that reason while they are in working order)

storage/space (a flat of bottles from Costco may use more area than a Britta, but they can be stored away from the sink or the refrigerator, on their sides, etc.)

and, incidentally,

the bottles themselves can be used again (filled with tap/Britta water for traveling, converted to rattles or pet toys, etc.)

In fact, having grown up in the city that was, until two or three years ago, the largest metropolitan area without fluoridation (making the choices buy fluoride drops or have lousy teeth), I would probably pay up for fluoridated bottled water.