When water boils, some of it turns into steam and floats away. That can slightly concentrate whatever is left behind, including minerals like fluoride. So you’re not removing it—you’re actually making the ratio of fluoride to water a tiny bit higher.
Think about a crowded elevator. If a few people get out, the remaining folks feel a little more crowded, right? Same idea here. The fluoride ions are the ones still standing in the elevator, and they have less water to swim around in.
Unless you boil your kettle until it’s bone-dry—which I really don’t recommend unless you want a very angry smoke alarm—the fluoride stays put. So no, boiling isn’t your fluoride-filtering hero.
