Fluoride is a naturally occurring mineral found in water worldwide. The short answer to whether fluoride dissipates in water is no: fluoride is highly stable and does not naturally evaporate, degrade, or dissipate over time. Its concentration remains constant unless the water undergoes active treatment to physically remove the substance.
Understanding Fluoride Stability in Water
The stability of fluoride in water is due to its chemical form once dissolved. Fluorine readily gains an electron to form the fluoride ion (F-), which is the form found in water. This ion is a dissolved solid, not a volatile compound that can easily turn into a gas.
Common environmental factors like boiling, freezing, or prolonged storage do not cause the fluoride ion to break down or escape. When water is boiled, the water molecules turn into steam, but the dissolved fluoride ions are left behind. This can slightly increase the concentration in the remaining water volume.
The strength of the ionic bond ensures that the resulting ion is not chemically reactive under normal conditions. The fluoride concentration in a specific volume of water stays the same unless an external mechanism is employed to physically separate it.
Natural and Added Sources of Fluoride
Fluoride enters the water supply through two distinct pathways: natural leaching and intentional addition. Naturally occurring fluoride originates from the dissolution of fluoride-containing rocks and minerals, such as fluorite, in the earth’s crust. As groundwater flows through these geological formations, it picks up and dissolves the fluoride ions, leading to varying concentrations in well water and other natural sources.
In municipal water systems, fluoride is often intentionally added in a controlled process known as water fluoridation. The purpose of this treatment is to adjust the concentration to a level considered optimal for dental health, typically around 0.7 parts per million. The most common compounds used for this purpose are fluorosilicic acid and sodium fluorosilicate, which quickly dissociate into the same stable fluoride ions (F-) found in naturally fluoridated water.
Technologies for Fluoride Removal
Since fluoride ions are stable and do not dissipate, active physical or chemical processes are required to reduce their concentration in drinking water. Consumers who wish to remove fluoride from their water supply rely on highly specific filtration technologies. These methods separate the dissolved fluoride ions from the water molecules, rather than waiting for the substance to break down.
Reverse Osmosis (RO) systems are one of the most effective ways to remove fluoride at the household level. This process works by forcing water under pressure through a semi-permeable membrane that has extremely small pores. The physical size of the fluoride ion, which is larger than a water molecule, causes it to be rejected by the membrane and flushed away in the wastewater stream. Well-maintained RO systems can remove between 95% to 99% of fluoride from the water.
Distillation is an alternative method that achieves high fluoride removal rates by exploiting the non-volatile nature of the ion. The process involves boiling the source water to produce steam, which is then collected and condensed back into liquid form. Because the fluoride ion is a dissolved solid with a significantly higher boiling point than water, it does not vaporize and is left behind. Home distillers can typically remove 95% to 99% of fluoride.
Another specialized method involves the use of Activated Alumina, a granular form of aluminum oxide that works through adsorption. Fluoride ions are chemically attracted to and bind with the surface of the alumina material as water passes through the filter bed. This process is highly dependent on the water’s pH, performing optimally in a slightly acidic range of 5.5 to 6.5. The effectiveness of Activated Alumina media eventually decreases as the surface becomes saturated with captured fluoride ions, requiring replacement or regeneration of the filter.