Can You Remove Fluoride By Boiling Water?

Pot of boiling water on stove top
Lew Robertson / Getty Images

Some people want fluoride in their drinking water, while others seek to remove it. One of the most common questions in chemistry relating to fluoride removal is whether you can boil fluoride out of your water. The answer is no. If you boil water or leave it on a hot plate for an extended period of time, the fluoride will become more concentrated, remaining in the water as a fluorine salt.

The reason is that you're not trying to boil out elemental fluorine, which is F2, but fluoride, F-, which is the ion. The boiling point of the fluoride compound — 19.5 C for HF and 1,695 C for NaF — doesn't apply because you're not dealing with the intact compound. Trying to boil out fluoride is akin to boiling out sodium or chloride from dissolved salt in water — it won't work.

Boiling to Distill Water to Remove Fluoride

However, you can boil water to remove fluoride if you capture the water that is evaporated and then condense it (distill it). The water you collect will contain much less fluoride than your starting water. As an example, when you boil a pot of water on the stove, the fluoride concentration in the water in the pot increases. The water that escapes as steam contains much less fluoride.

Methods That Remove Fluoride From Water

There are effective methods to remove fluoride from water or lower its concentration, including:

  • Distillation: boiling the water, collecting the vapor, and chilling the vapor until it forms liquid water
  • Reverse osmosis: forcing water through a semipermeable membrane, leaving the fluoride and other ions on one side of the membrane, with higher purity water on the other side.
  • Activated alumina: running water across activated alumina (aluminum oxide), which captures the fluoride so the water has a lower ion concentration.

Methods That Do Not Remove Fluoride

These methods do not remove fluoride from water:

  • As mentioned, normal boiling does not remove fluoride. It increases its concentration.
  • Most water filters don't touch fluoride.
  • Freezing water doesn't remove fluoride.

Fluoride lowers the freezing point of water (freezing point depression), so ice from fluoridated water will be higher purity than the source water, providing some liquid remains. Similarly, icebergs are freshwater rather than saltwater. The fluoride ion concentration is low, so using freezing to purify water is impractical. If you freeze a tray of fluoridated water into ice, the ice will have the same fluoride concentration as the water.

Fluoride concentration is increased after exposure to nonstick cookware. Nonstick coating is a fluorine compound, which leaches slightly into water and foods.

mla apa chicago
Your Citation
Helmenstine, Anne Marie, Ph.D. "Can You Remove Fluoride By Boiling Water?" ThoughtCo, Aug. 27, 2020, Helmenstine, Anne Marie, Ph.D. (2020, August 27). Can You Remove Fluoride By Boiling Water? Retrieved from Helmenstine, Anne Marie, Ph.D. "Can You Remove Fluoride By Boiling Water?" ThoughtCo. (accessed July 29, 2021).